This study was conducted to examine early gonadogenesis by using a histological method for the appearance of primordial germ cells (PGCs), protrude of genital ridge, and formation of primitive gonads in diploid and triploid mud loach, Misgurnus mizolepis. The pattern of early gonadogenesis including appearance of PGCs, formation of genital ridge, and development of primitive gonad in both diploid and triploid were not different histologically. Characteristics of PGCs of triploid were also the same as those of diploid. However, gonadal length of diploid was significantly longer than that of triploid (P<0.05).