The common house fly, Musca domestica L., was assessed for its potential as a mechanical carrier of bacteria in urban areas of Chiang Mai province, north Thailand. Sixty-one specimens (61.0%) were found to carry bacteria, with each harboring 1-5 bacteria. No significant difference between the sex of flies for carrying bacteria was found. A total of 21 bacteria was isolated, of which the most common was coagulase negative staphylococci (n = 38), followed by Viridans streptococci (n = 9). The highest bacterial load for all bacteria isolated was 10(3)-10(4) (67%), followed by > 10(4) (26%) colonies per fly. It is recommended that fly control management measures, including sanitation improvement, should be implemented.