Eocasea is an extinct genus of caseid synapsids from the Late Pennsylvanian of Kansas.

Caseids are notable for being one of the first groups of tetrapods to evolve herbivory; large-bodied taxa such as Casea and Cotylorhynchus have barrel-shaped rib cages and leaf-shaped, serrated teeth that are clear adaptations for breaking down plant cellulose.

Eocasea differs from these taxa in having a narrow rib cage, simple cone-shaped teeth, and a much smaller body size.

All of these are plesiomorphic features for synapsids, meaning that Eocasea inherited a carnivorous lifestyle from similarly small-bodied carnivorous ancestors of synapsids.

As the earliest known caseid, Eocasea represents one of the first transitions from carnivory to herbivory in tetrapods.