前鳃亚纲（学名：Prosobranchia）是腹足纲之下的一个弃用生物分类，其物种现时已散落到其他分类。

本亚纲的物种从海螺、蜗牛及淡水螺均有。「前鳃亚纲」这名称的出现可追溯至1920年代，取名于本物种「鳃在心脏的前方」，与后鳃亚纲相对。事实上，前鳃亚纲物种不单其鳃，就连其套膜及肛门均位于心脏之前，而且雌雄不同体。这个分类及至后来支序生物学兴起，才发现原来是个多系群，因此本分类变得不再合适，而要重新分类。尽管如此，由于这分类的原来物种的解剖结构特色，「前鳃类」这个名字仍然在软件动物学很常见。即使在古生物学，一些难以被分类的物种，亦会基于其解剖结构而暂时归入本分类。

Not to be confused with the bivalve order Protobranchia.

Prosobranchia was a large taxonomic subclass of sea snails, land snails and freshwater snails. This taxon of gastropods dates back to the 1920s. It has however been proven to be polyphyletic (consisting of more than one lineage of descent). Generally speaking in biology taxonomy is required to reflect phylogeny, in other words the classification of a group must reflect its evolutionary descent, as far as that is known, so the taxon Prosobranchia is no longer considered suitable to be used.