决明（学名：Cassia obtusifolia），又名草决明、马蹄决明、假绿豆，属豆科决明属。原产于中国长江以南各省区，现在整个美洲、亚洲、非洲、大洋洲都有分布。

决明子是「决明」的种子，为常用中药，种子入药，具有清肝明目、通便的功能。主治高血压、头痛、眩晕、急性结膜炎、角膜溃疡、青光眼、痈疖疮疡等症。用其叶泡茶，中老年人长期饮用，可使血压正常，大便通畅。

决明在植物群落里生命力极其旺盛，常常与其他植物争夺营养，因此在北美洲等地区，决明被视为一种难以根除的野草。

"Cassia humilis" redirects here. This taxon may also refer to other species; see below.

Senna obtusifolia (Chinese senna, American sicklepod or sicklepod) is a legume in the genus Senna, sometimes separated in the monotypic genus Diallobus. It grows wild in North, Central, and South America, Asia, Africa, and Oceania, and is considered a particularly serious weed in many places. It has a long-standing history of confusion with Senna tora and that taxon in many sources actually refers to the present species.