House dust mite of the indoor environment is one of the most important causes of allergic asthma and rhinitis. It has been known that more than 70% of Korean children and about 50% of adult with the respiratory allergy are sensitive to house dust mite. The purpose of our study is to find out the relationship between the concentration of formaldehyde (HCHO)/PM10 and the number of house dust mite in the indoor environment. In this study, sampling sites were education, social and dwelling facilities. We inquire the questionnaire of the resident on the indoor air quality in all sampling sites. At the same time, we measured the concentration of formaldeh yde(HCHO)/PM10 as well as house dust mites. it was complained by 20% respondents that the indoor air quality was bad and by 10% that the atopy symptom was evident. When a certain amount of house dust mites were detected, the contents of PM10 were observed high and that of HCHO low. However when the house dust mites were not detected, the concentration of PM10 was low and that of HCHO high. From our results, it is concluded that the indoor air quality (i.e. conc. of PM10/HCHO) is quite related to the contents of house dust mites supporting the fact that the symptom of atopy and asthma is due to these small organisms. Keywords : House dust mite, Indoor environment, HCHO, PM10, Atopy