An analysis method of tetracyclines far fish and shellfish products containing large amount of low molecular materials and pigments was established. The recovery of the established analysis method for four tetracycline samples was $72-100\%$ and higher than other methods reported. Especially, proposed sample treatment protocol was shown to be effective for the removal of low molecular materials and pigments that tend to interfere with accurate analysis. The detection limit of oxytetracycline (OTC) and tetracycline (TC) from the sample was 0.02 ppm, and the detection limit of chlortetracycline (CTC) and doxycycline (DC) from the sample was 0.1ppm, To examine the efficiency of the established method and identify tetracycline usage in fish farms, tetracycline group antibiotics in the flounder being cultured was monitored. The improved method can be used for fish and shellfish products effectively and all surveyed fish farms have used tetracycline all the year round. The proposed method was adopted as official method for fishery products by Korean Food and Drug Administration in 2003 and it is being used by regulatory authority as National Fishery Products Quality Inspection Service.