Moja soba je mala, ali lepa.

Because soba is a feminine singular noun, and the possessive adjective moj must agree with it.

Agreement in Serbian means the possessive changes form to match the noun's:

• gender
• number
• case

Here:

• soba = feminine
• singular
• nominative case

So moj becomes moja.

Compare:

• moj stan = my apartment/flat (stan is masculine)
• moja soba = my room (soba is feminine)
• moje selo = my village (selo is neuter)

A very common clue is the ending -a. Many Serbian nouns ending in -a are feminine.

So:

• soba = room, feminine
• kuća = house, feminine
• škola = school, feminine

This is not a perfect rule for every noun in the language, but it works very often and is a good beginner guideline.

You can also see that the other words agree with it:

• moja
• mala
• lepa

All of those are feminine singular forms, which confirms that soba is feminine.

Because they are adjectives agreeing with soba, which is feminine singular.

In Serbian, adjectives change form to match the noun they describe.

So:

• mali = small, masculine form
• mala = small, feminine form
• malo = small, neuter form

And similarly:

• lep = beautiful/nice, masculine
• lepa = beautiful/nice, feminine
• lepo = beautiful/nice, neuter

Examples:

• Moj stan je mali. = My apartment is small.
• Moja soba je mala. = My room is small.
• Moje selo je malo. = My village is small.

Je means is. It is the 3rd person singular present tense form of the verb biti = to be.

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In your sentence:

• Moja soba je mala, ali lepa.
• literally: My room is small, but beautiful.

So je links the subject moja soba with the description mala, ali lepa.

Usually in a normal present-tense sentence like this, no. You need it.

So:

• Moja soba je mala. = correct
• Moja soba mala. = not standard Serbian

Serbian sometimes drops forms of to be in specific styles or structures, but for a basic sentence like this, learners should keep je.

Because Serbian does not have articles like English.

English distinguishes:

• a room
• the room
• my room

Serbian does not use separate words like a or the. Context tells you what is meant.

So:

• soba can mean a room or the room, depending on context
• moja soba means my room

The possessive moja already makes it specific, so English naturally uses my room.

Because ali means but, and in Serbian it is normally preceded by a comma when it joins two contrasting parts of a sentence.

So:

• Moja soba je mala, ali lepa.

This is very similar to English punctuation:

• My room is small, but beautiful.

The comma marks the contrast between:

• mala = small
• lepa = beautiful/nice

In this sentence, ali means but.

It introduces a contrast:

• the room is small
• but it is also beautiful/nice

That is the most common meaning of ali. It is a very useful everyday conjunction.

Examples:

• Umoran sam, ali srećan. = I am tired, but happy.
• Nije skup, ali je dobar. = It is not expensive, but it is good.

It can mean either, depending on context.

Lep / lepa / lepo often means:

• beautiful
• pretty
• nice
• lovely

For a room, English might translate it as:

• beautiful
• nice
• lovely

So Moja soba je mala, ali lepa could sound like:

• My room is small, but beautiful.
• My room is small, but nice.

The exact English choice depends on tone and context.

Because lepa describes soba, which is feminine.

Lepo is either:

• the neuter adjective form, or
• sometimes an adverb meaning nicely

Here you need the feminine adjective:

• soba = feminine
• therefore lepa

Compare:

• Lepa soba = a beautiful room
• Lepo dete = a beautiful/lovely child (dete is neuter)
• On lepo peva. = He sings nicely. (lepo as an adverb)

The basic word order here is very natural:

• Moja soba je mala, ali lepa.

But Serbian word order is more flexible than English, and changes can add emphasis.

For example:

• Moja soba je mala, ali lepa. = neutral
• Mala je moja soba, ali lepa. = more emphasis on small
• Moja soba je lepa, ali mala. = same grammar, but the emphasis/contrast changes because now beautiful comes first

For learners, the original order is the safest and most natural.

Yes. That would simply mean:

• The room is small, but beautiful or
• A room is small, but beautiful

depending on context.

Adding moja makes it specifically my room.

So:

• Soba je mala, ali lepa. = The room is small, but beautiful.
• Moja soba je mala, ali lepa. = My room is small, but beautiful.

Because here they are predicate adjectives, not adjectives placed directly before the noun.

There are two common patterns:

1. Attributive adjective: directly before the noun

   • moja mala soba = my small room
   • lepa soba = a beautiful room

2. Predicate adjective: after je

   • moja soba je mala = my room is small
   • moja soba je lepa = my room is beautiful

In your sentence, the structure is:

• subject: Moja soba
• verb: je
• description: mala, ali lepa

Yes, depending on the regional standard.

• In Serbian Ekavian, you usually get lepa
• In Ijekavian varieties, you may see lijepa

So these are equivalent by region/standard:

• Moja soba je mala, ali lepa.
• Moja soba je mala, ali lijepa.

A learner of standard Serbian in Serbia will most often meet lepa.