在集合论中，空集公理是 Zermelo-Fraenkel 集合论的公理之一。

在 Zermelo-Fraenkel 公理的形式语言中，这个公理读做:

换句话说:

有着一个集合使得没有集合是它的元素。

In axiomatic set theory, the axiom of empty set is an axiom of Kripke–Platek set theory and the variant of general set theory that Burgess (2005) calls "ST," and a demonstrable truth in Zermelo set theory and Zermelo–Fraenkel set theory, with or without the axiom of choice.