A direct competitive enzyme−linked immunosorbent assay(ELISA)for screening sulfamethazine(SMZ)in pork tissues was developed.The assay was made with the affinity−purified polyclonal antibody−coated microtiter plate.A cross reactivity of IgG was observed at 3.5 μg/g of sulfamerazine among nine kinds of sulfonamide tested.Pork tissues fortified with SMZ was mixed with octadecyl silica(C₁₈), and extracted with dichloromethane.The extracted SMZ was measured by homemade ELISA, commercial ELISA, and HPLC.The results were correlated(r=0.993, p<0.01).The homemade ELISA was sensitive to determine SMZ at the maximum residue level(MRL)as commercial one.During stability test of the IgG coated microtiter plate performed at 40°C for 14 days, no difference in sensitivity was observed.We developed homemade ELISA with a detection limit of 10 ng of SMZ per g of pork tissues, and it could be used to screen SMZ in pork tissues.