У меня есть один брат.

I have one brother.

Breakdown of У меня есть один брат.

• я: I
• брат: the brother
• один: one

Questions & Answers about У меня есть один брат.

Why is меня in the genitive case rather than nominative in У меня есть один брат?

In Russian possession is shown with У + genitive + есть (“at someone there is”). The preposition у always requires the following pronoun or noun to be in the genitive case, so я becomes меня.

Why is есть used in this sentence, and what exactly does it mean?

Есть is the 3rd-person singular present of быть (“to be”) and here functions like English there is. The phrase У меня есть literally means “at me there is,” which we translate as “I have.”

Could we drop есть and say У меня один брат? Would the meaning change?

Yes—omitting есть is common in informal Russian. У меня один брат still means “I have one brother.” Including есть can sound slightly more formal or emphatic, but both forms are correct.

What role does один play in У меня есть один брат? Is it necessary?

Один means “one” and specifies the exact number. You can say У меня есть брат (“I have a brother”) without один, which implies you have at least one brother. Adding один makes it clear you have exactly one.