自反关系是在逻辑学和数学中一种特殊的二元关系，这样的二元关系被称为自反的，也被称为具有自反性。

集合X，以及其上的二元关系R，若满足：∀a∈X，有aRa。则称二元关系R是自反的，或称R具有自反性，或称R为自反关系。

In mathematics, a binary relation R over a set X is reflexive if every element of X is related to itself.

In mathematical notation, this is:

An example of a reflexive relation is the relation "is equal to" on the set of real numbers, since every real number is equal to itself. A reflexive relation is said to have the reflexive property or is said to possess reflexivity.