SRY gene is normally responsible for testis induction, yet testis development can occur in the absence of SRY. In here, we analyzed the SRY-negative sex reversal in cocker spaniel, at 1.5 year-old. The attacked dog was suffered from enlarged clitoris, and resulted in disorder of urination. By surgically approach, enlarged clitoris and one testis, which are apparently seen, are removed. Additionally, thorough the abdomen surgery, uterus and ovary-like mass were removed. The dog had XX, chromosome, showed negative for SRY-gene, and the mass had the ovary-testis structure. In other words, based on the macroscopic, cytogenic, and histological study, we can diagnose the cocker spaniel as SRY-negative sex reversal.