This study describes the developmental process of gonads in chameleon goby, Tridentiger trigonocephalus from the stage of hatching to 100 days after hatching (DAH). Based on histological observation, the primordial germ cells were observed in mesentery between mesonephric duct and gut at 15 DAH (total length, TL: $6.8{pm}0.2mm$). At 20 DAH (TL: $7.9{pm}0.1mm$), the primordial gonad began to protrude into peritoneal cavity and developed between mesonephric duct and gut. Initial ovarian differentiation was identified by the presence of ovarian cavity and oogonia in the gonads at 55 DAH (TL: $21.1{pm}1.3mm$). Testicular differentiation started at 65 DAH (TL: $23.7{pm}0.9mm$) with appearance of spermatogonial cells in the gonads. These findings indicate that sex differentiation in T. trigonocephalus occurs earlier in females than males, suggesting that this species can be classified as an undifferentiated gonochorist.