Technical Abstract: Infection with Sarcocystis species is common in hervibores but is rare in bears. Histological sections of 374 black bears (Ursus americanus) from Pennsylvania were examined for sarcocysts. A total of 3 sarcocysts were found in 3 bears, 1 sarcocyst per section. Sarcocysts from 2 bears were considered a new species and named Sarcocystis ursusi. Sarcocysts of S. ursusi were microscopic and contained only bradyzoites. By light microscopy, the sarcocyst wall was thin (<0.5 um thick) and had minute serrations on the sarcocyst wall. Ultrastructurally, the serrations on the sarcocyst wall consisted of villar protrusion (Vp) that were mostly 0.5 um long. The Vp had bundles of electron-dense microtubules that were as wide as the villar protrusions and these microtubules extended deep in to the ground substance layer, a feature that distinguished this species from unnamed sarcocysts from black bear. Bradyzoites were 4.8-6.0 um long. The sarcocyst from the third bear was structurally different from S. ursusi; its sarcocyst wall was approximately 2 um thick and had finger-like villi on the cyst wall giving the sarcocyst wall a striated appearance.