Erythromycin has been used to treat Streptococosis, Edwardsiel1osis, Vibriosis, Bacterial enteritis in the cultured fish. In this study, a rapid and effective erythromycin analysis method with new sample treatment protocol and liquid chromatography/tandem mass spectrometry (LC/MS/MS) system for fish products was developed. For the erythromycin extraction from fish muscle, the solvent mixture composed of 0.2% meta-phosphoric acid and methanol (6:4) showed good recovery rate, and the optimum extraction solvent volume was 20 mL. Erythromycin detection using LC/MS/MS were carried out under electro spray ionization (ESI) positive condition and erythromycin mass value 576.2 and 157.9. And the detection limit of the established method was 0.005 mg/kg in fish products. The recovery rate of the developed method applied to the fish species were as following, olive flounder, $87.6{pm}5.0%$; black rockfish, $87.2{pm}6.4%$; eel, $85.2{pm}4.8%$; and rainbow trout, $86.0{pm}6.2%$. In the established method in this study, the correlation of coefficient values ($R^2$) of erythromycin calibration curve (n=11) was 0.9998.