桉树（英语：Eucalyptus）又名尤加利树，是桃金娘科桉属植物的总称。

一般为常绿乔木；枝、叶花有芳香；叶子通常互生，有柄，全缘羽状脉，多为镰刀形；早春开白色、红色或黄色花，多为伞形或头状花序，萼片与花瓣连合成帽状体（花盖），开花时脱落；蒴果成熟时顶端3－5裂；种子多数有角棱。

Eucalyptus /ˌjuːkəˈlɪptəs/ L'Heritier 1789 is a diverse genus of flowering trees and shrubs (including a distinct group with a multiple-stem mallee growth habit) in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia. There are more than 700 species of eucalyptus and most are native to Australia, and a very small number are found in adjacent areas of New Guinea and Indonesia. One species, Eucalyptus deglupta, ranges as far north as the Philippines. Only 15 species occur outside Australia, with just nine of these not occurring in Australia. Species of eucalyptus are cultivated widely in the tropical and temperate world, including the Americas, Europe, Africa, the Mediterranean Basin, the Middle East, China, and the Indian subcontinent, though most species do not tolerate frost.