Formal:
* Il a un petit nez. (This is the most literal and neutral translation.)
Informal:
* Il a le nez fin. (This translates to "he has a fine nose" and implies a delicate and elegant feature.)
* Il a un nez minuscule. (This emphasizes the small size of his nose.)
* Il a un nez tout petit. (This is similar to the previous option but adds an endearing touch.)
More colloquial:
* Il a un nez de bouton. (This literally means "he has a button nose" and is often used humorously.)
The best option will depend on the context and the level of formality you want to use.