双小行星是两颗小行星环绕着它们共同质量中心的系统，类似于联星。伽利略号在1993年飞越(243) Ida，首度证实它是一对双小行星，之后又检测到许多双小行星。

当双小行星的两颗有着相似的大小时，它们有时会被称为“Binary companions”、“Double asteroids”或“Doublet asteroids”。(90) Antiope 就是真实的双小行星的好例子。与小卫星，称为小月球，组成的双小行星更常被观测到 (参见(22) Kalliope、(45) Eugenia、(87) Sylvia、(107) Camilla、(121) Hermione、(130) Elektra、(243) Ida、(283) Emma、(379) Huenna等等)，他们也称为大小比例悬殊的高尺寸比双小行星。

A binary asteroid is a system of two asteroids orbiting their common barycenter. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993. Since then numerous binary asteroids have been detected.

The mass ratio of the two components of a binary system is an important characteristic. Most binary asteroids have a large mass ratio, i.e. a relatively small satellite in orbit around the main component. Systems with a small satellite, or "moon", include 22 Kalliope, 45 Eugenia, 87 Sylvia, 107 Camilla, 121 Hermione, 130 Elektra, 243 Ida, 283 Emma, and 379 Huenna. Some binary systems have a mass ratio near unity, i.e. two components of similar mass. They include 90 Antiope and Hermes.