蜥形纲（学名：Sauropsida）是羊膜动物的一大演化支，包含了所有现存爬行类与鸟类。

与本纲最亲近的外类群就是合弓纲；合弓纲由似哺乳爬行动物与哺乳纲的最近共同祖先及其所有后代组成。两纲一起组成羊膜动物。

Sauropsida ("lizard faces") is a group of amniotes that includes all existing reptiles and birds as well as their fossil ancestors and other extinct relatives. Large land animals are either in this group or in its sister group, Synapsida, which includes mammals and their fossil relatives. This clade includes Parareptilia and other extinct clades. All living sauropsids are members of the sub-group Diapsida, the Parareptilia clade having died out 200 million years ago. The term originated with Thomas Henry Huxley, who grouped birds with reptiles based on fossil evidence.