Severe coccidiosis was found in sections of small intestine of a less than 2 day old lion (Panthera leo) born in captivity. Schizonts, merozoites, gamonts, and unsporulated oocysts were located in epithelial cells of ileum. Ultrastructural examination indicated that schizonts divided by schizogony. Merozoites were 5.1-7.0 × 1.4-1.6 μm in size and contained numerous micronemes arranged in rows. The rhoptries had a long neck with long bulbous ends that were turned around in a loop. Organisms did not stain with antibodies to Toxoplasma gondii and Neospora caninum. This is the first report of intestinal coccidiosis in a neonatal lion.