Aleksej (Serbian Cyrillic: Алексеј) is a Serbo-Croatian and Belarusian masculine given name, a variant of Greek Alexis and Alexios (Latinized form Alexius). The name Aljoša is a diminutive of the name. It may refer to:
- Aleksej Aleksandrov, Belarusian chess player
- Aleksej Nešović, Serbian basketball player
- Aleksej Nikolić, Slovenian basketball player
- Aleksej Pokuševski, Serbian basketball player