Objective: To examine sex reversal both by oral and by immersion using 17-methyltestosterone on the methyltestosterone residual concentration and the organ histopathology of tilapia fish. Methods: This study used oral and immersion treatment methods for sex reversal of tilapia fish and used normal fish as the control and each treatment was repeated 4 times. 17-methyltestosterone at dosages of 60 mg/kg feed and 0.5 mg/L were used for oral and immersion methods, respectively. In the first step, tilapia fry were reared at 100 L aquaria, with a density of 1 fish/L for 2 months. In the next step, male tilapias were reared at happa (net cage) of (2×1×1) m3 size in the controlled pond, with a density of 30 fish/happa for 3 months. The methyltestosterone residual concentrations were analyzed by one-way analysis of variance and Duncan's multiple range tests, while organ histopathology was analyzed by descriptive method. Results: Residual concentrations in the serum of methyltestosterone-treated fish were significantly lower than that in normal fish, especially in 4-and 5-month-old tilapias with averages of less than 5 μg/L, while in normal fish was more than 5 μg/L. In the flesh, methyltestosterone residual concentrations showed relatively no significant differences between the oral and immersion treatment groups and methyltestosterone-Treated fish remained lower compared to normal fish, except in 5-month-old tilapia. Methyltestosterone-Treated tilapia exhibited histopathological changes on gill, liver, kidneys, and intestine organs. Conclusions: Sex reversal either by oral or by immersion has methyltestosterone residual concentration, but does not exceed the limits (5 μg/L or 5 μg/kg) of synthetic steroid on the fish body, although methyltestosterone causes histopathological changes on gill, liver, kidneys, and intestine.