This report provides histological information on the incidental finding of tetrathyridium in the testicles of a three-year-old cross-bred cat. The cat was chemically castrated by intratesticular injection of calcium chloride (CaCl2). Bilateral orchiectomy was performed and no gross lesions were seen in the testicles. Histological evaluation of right testicle revealed tetrathyridium with convoluted borders and a thick eosinophilic cuticle. The stroma of the parasitic body was composed of a loose mesenchymal network with widely scattered parenchymal and muscle cells, and numerous clear vesicles (calcereous corpuscles). Thus, the case was evaluated as intratesticular tetrathyridiosis. To our knowledge, this is the first descriptive report of intratesticular tetrathyridiosis in a cat.