The insecticide resistance of field Musca domestica collected from 7 different populations of different habitats in seven administrative areas of Tianjin was determined by spot drip method and compared with the relatively sensitive strain in the laboratory. The individual carboxylesterase and glutathione S-transferase activity of populations from different areas were determined. The results indicated that the populations from different areas had different resistance levels to the insecticides tested. The resistance level to DDVP varied from 1.885 to 18.563 times, the resistance level to high effect cypermethrin varied from 1.071 to 14.071 times and the resistance level to propoxur varied from 1.071 to 7.499 times. The average activity of carboxylesterase of the field flies were higher than that of houseflies of the relatively sensitive strain in the laboratory. The distribution of carboxylesterase activity in both sensitive and field populations were obviously overlapped. The glutathione S-transferase activity of F₂ generations were quite different. The glutathione S-transferase activity of the field populations were higher  than that of the relatively sensitive strain in the laboratory, varied regionally from 2 to 4 times, which was in accordance with the diversity of the insecticide resistance levels of M. domestica in different areas in Tianjin.