Achoetandrus rufifacies (Macquart) (Diptera: Calliphoridae) is the important blow fly species of medical concern in Thailand. The adults are mechanical vectors of various pathogens, while the larvae can cause myiasis. Regarding this, a method to control fly population is mandatory, with all aspects of the basic research of this fly species being needed. In this study, we investigated the response of this fly species to climatic and physio-environmental factors in Chiang Mai, northern Thailand. Adult fly surveys were carried out every two weeks from July 2013- June 2014 at study sites in Mae Hia Agricultural Research, Demonstrative and Training Center using automatic baited trap with 1-day tainted beef offal as bait. A total 55,988 adult A. rufifacies were captured, with peak densities being observed in summer, followed by rainy season and winter. Population density had positive correlation with temperature (r = 0.461), but negative correlation with relative humidity (r = 0.621). The daily activity showed major peak during 15.00 – 18.00 pm. Changes in the ovariole during egg development of this species were conducted from day 1 to day 9. As has been proposed in the grant proposal, the extra researches were conducted for biological information of other medically important flies, if species were available from the field collections. In this regard, seasonal and daily activity of blow fly, Chrysomya megacephala were conducted, of which the experimental design was the same as that has been described in A. rufifacies. Peak population was found in summer, followed by rainy season and winter. The daily activity showed major peak during 15.00 – 18.00 pm. Biological investigation in the laboratory revealed that females of this species can oviposit upto 7 times in her lifetime. Moreover, molecular identification of blow flies of medical importance in Thailand was performed using COI gene. Information gained from this thorough study in both alimentary and reproductive systems established a basic database, which was useful in understanding their functional role and serving as knowledge to address a strategy to control this fly species in the future.