Ovaj deo je mali.

Because ovaj has to agree with deo in gender, number, and case.

• deo is a masculine singular noun
• the sentence uses the nominative case, because deo is the subject
• so the correct form is ovaj

Compare:

• ovaj deo = this part (masculine)
• ova knjiga = this book (feminine)
• ovo selo = this village (neuter)

So ovaj is simply the masculine nominative singular form of this.

It is in the nominative singular.

In Ovaj deo je mali, ovaj deo is the subject of the sentence: This part. Subjects normally appear in the nominative case in Serbian.

So:

• ovaj = nominative masculine singular
• deo = nominative singular

They match because they belong together as one noun phrase.

Because adjectives in Serbian also have to agree with the noun they describe.

Since deo is:

• masculine
• singular
• nominative

the adjective must also be:

• masculine
• singular
• nominative

So you get mali.

Compare:

• ovaj deo je mali = this part is small
• ova kuća je mala = this house is small
• ovo dete je malo = this child is small

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

So:

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

In this sentence:

• Ovaj deo je mali = This part is small

The word je connects the subject and the description, just like is in English.

Normally, no. In a standard sentence like this, je should be there.

• Ovaj deo je mali. = correct
• Ovaj deo mali. = not normal standard Serbian

You may see omission in headlines, notes, poetry, or very informal shorthand, but for normal speech and writing, keep je.

No, Serbian does not have articles.

That means Serbian does not directly mark the difference between:

• a part
• the part

in the way English does.

Instead, Serbian uses context, word order, and words like demonstratives.

Here, ovaj deo specifically means this part, because ovaj is a demonstrative. If you said just deo, it could mean a part or the part, depending on context.

A simple learner-friendly pronunciation is roughly DEH-oh.

The important thing is that both vowels are heard:

• de-o

Do not reduce it to one English-style vowel sound.

Also, learners often notice another form, dio. That is a regional/standard variant used outside Ekavian Serbian. In standard Serbian as spoken in much of Serbia, deo is normal.

Yes, Serbian word order is more flexible than English, but this version is the most neutral and straightforward.

• Ovaj deo je mali. = neutral, standard
• Mali je ovaj deo. = more marked, like This part is the small one or with emphasis
• Ovaj mali deo... would mean this small part... if mali were placed before the noun

So the given sentence uses the most basic pattern:

• subject
  • je
    • adjective

This is a very useful distinction.

• Ovaj deo je mali. = This part is small.

  • Here mali is the main description of the sentence.
  • It comes after je.

• Ovaj mali deo = this small part

  • Here mali is inside the noun phrase and directly modifies deo.

So:

• after je: predicate adjective
• before the noun: attributive adjective

Yes. This is something that often surprises English speakers.

Many Serbian nouns ending in -o are neuter, but deo is masculine. Its grammatical gender is something you simply learn with the word.

That is why it takes:

• ovaj not ovo
• mali not malo

So even though the ending may look misleading at first, the agreement shows you clearly that deo is masculine.

You make it negative by changing je to nije:

• Ovaj deo nije mali. = This part is not small.

That is the normal way to negate is in Serbian.

Yes.

• Deo je mali. = The part is small / A part is small, depending on context
• Ovaj deo je mali. = This part is small

Adding ovaj makes the reference more specific and points to something near the speaker or already being indicated.

The plural would be:

• Ovi delovi su mali. = These parts are small.

Notice all the changes:

• ovaj → ovi
• deo → delovi
• je → su
• mali stays mali in masculine plural

This is a good example of how several words in Serbian change together to show agreement.