In some catarrhines, tails have extremely reduced. In order to clarify the tail reduction process in the catarrhines, understanding the sacro-caudal musculo-skeletal morphological variations with different tail lengths is essential. Although previous studies revealed that skeletal morphology strongly reflected tail length variation, caudal musculature has scarcely been studied. Thus, this study aimed to increase the knowledge about caudal musculature in catarrhines. Comparative dissection of both the dorsal and ventral side of the lumbo-sacro-caudal region in five individuals of five catarrhine species was performed, and following findings were obtained: 1) All caudal muscles tended to insert or become tendinous more cranially in shorter tailed species, 2) Ventral caudal flexors were completely lost in catarrhines with shorter tails than M. arctoides, 3) Pelvocaudal muscles were present regardless of the tail length, 4) Only one kind of dorsal caudal extensor muscle was observed in very short tails species and were lost in tailless species, and 5) Dorsal caudal abductors existed independently in all of tailed species and were lost in tailless Pan troglodytes. Together with the skeletal morphological perspective, these findings will be helpful for understanding the tail reduction process in catarrhines in the future.