Non-Alchemists: Because Homunculi do not have souls, they are incapable of opening the Gate inside them and are thus unable to perform alchemy.

Can homunculus use alchemy brotherhood?

In Fullmetal Alchemist Brotherhood, we saw that the core of a homunculus is a philosopher's stone, but ironically, they still can't perform any alchemy.

What is a homunculus in alchemy?

A homunculus (UK: /hɒˈmʌŋkjʊləs/ hom-UNK-yuul-əs, US: /hoʊˈ-/ hohm-, Latin: [hɔˈmʊŋkʊlʊs]; "little person") is a representation of a small human being. Popularized in sixteenth-century alchemy and nineteenth-century fiction, it has historically referred to the creation of a miniature, fully formed human.