Nasa akin ang susi mo.

Nasa here means something like is at / is with / is in the possession of.

In this sentence, Nasa akin ang susi mo is a very natural Filipino way to express I have your key or Your key is with me.

A useful thing to know:

• nasa is commonly understood as na sa
• sa is a preposition meaning things like in, at, to, with, depending on context

So nasa akin literally feels like is with me / is at me, which becomes I have it in natural English.

Because akin is the form used in a sa phrase.

Filipino pronouns change form depending on their role in the sentence. For I / me / my, the common forms are:

• ako = I
• ko = my / by me
• akin = mine / me in certain constructions, especially after sa

Since the sentence has sa inside nasa, the correct form is sa akin, not sa ako or sa ko.

So:

• nasa akin = with me
• not nasa ako
• not nasa ko

Ang marks the topic of the sentence.

Here, ang susi mo is the thing being talked about:

• ang = topic marker
• susi mo = your key

So the structure is roughly:

• Nasa akin = is with me
• ang susi mo = your key

Filipino does not always work like English subject + verb + object. Instead, it often marks the main noun phrase with ang.

Because Filipino very often puts the predicate first.

In this sentence, the predicate is nasa akin. The topic, marked by ang, comes after it:

• Nasa akin = predicate
• ang susi mo = topic

So Nasa akin ang susi mo is a normal, natural order.

You can also say:

• Ang susi mo ay nasa akin

That version is also correct, but it has a slightly more formal or more explicitly structured feel.

Because in Filipino, a possessive pronoun usually comes after the noun it possesses.

So:

• susi mo = your key
• bahay ko = my house
• kaibigan niya = his/her friend

This is the normal pattern:

• noun + possessive pronoun

So susi mo is correct, while mo susi is not.

Yes, very much so.

Filipino often expresses possession by saying that something is with someone rather than using a direct verb like English have.

So instead of thinking:

• I have your key

Filipino often thinks more like:

• Your key is with me

That is why Nasa akin ang susi mo sounds natural.

Other related ways to express possession exist, but for a specific item that is in your possession, this sentence is excellent and very common.

Not necessarily.

Nasa akin usually means the key is in your possession or with you, but it does not always mean it is literally in your hand.

For example, it could be:

• in your pocket
• in your bag
• at your house
• somewhere you are keeping it

If you want to emphasize that you are literally holding it, you might use a different expression such as hawak ko ang susi mo.

So nasa akin is broader than I’m holding it.

Yes.

Ang susi mo ay nasa akin and Nasa akin ang susi mo mean the same thing.

The difference is mainly in style:

• Nasa akin ang susi mo = very natural, common, conversational
• Ang susi mo ay nasa akin = also correct, a bit more formal or deliberate

The word ay is often used in sentences where the topic comes first.

You may see both nasa and na sa.

In modern everyday writing, nasa as one word is very common. That is why Nasa akin ang susi mo looks perfectly normal.

Learners should recognize that:

• nasa akin
• na sa akin

can represent the same basic idea in many contexts.

In practice, nasa is the form you will often encounter.

They are related, but they do not work the same way.

• akin by itself can mean mine
• sa akin can mean to me, for me, with me, or at my place, depending on context

In your sentence, the meaning comes from the full expression nasa akin, not from akin alone.

So here you should understand it as a set phrase:

• nasa akin = is with me / is in my possession

Not just mine by itself.

No, not in this sentence.

Here is why:

• ang is used for the topic phrase
• si is used mainly for personal names
• ng marks a different grammatical role and would change the structure

Since susi mo is not a person’s name, si is impossible here. And ng susi mo would not fit the sentence pattern you have.

So ang susi mo is the correct form.