In this study, we analyzed the factors affecting the concentration of airborne asbestos fiber in the indoor and outdoor environment of a slate roofing house, and performed a health risk assessment of residents living in houses with slate roofs. Sampling was conducted at ten houses with slate roofs on 3 different days under different weather conditions. A high flow rate pump was used for sampling. The specimen was assessed using a phase-contrast microscope. The degree of risk of exposure to asbestos was assessed using EPA’s carcinogen risk assessment method. Asbestos fiber concentrations for slate roofing houses were 2.43 fiber/L inside and 2.46 fiber/L outside, respectively. The correlation between the indoor and outdoor asbestos fiber concentration was 0.486. But on both sides, the asbestos fiber concentrations did not exceed the standard (10 fiber/L) for ambient air in Korea. The factors affecting the concentration of asbestos fiber were year of construction (p<0.05), total roof area (p<0.05) and average wind velocity (p<0.01). According to EPA’s ELCR (Excess Lifetime Cancer Risk) on air pollution substances, a level of 1.0E-04~1.0E-06 should be maintained. However, the ELCR level of 6 out of 10 houses was over 1.0E-04. Therefore, a risk management plan for residents of slate roofing houses must be prepared immediately. Keywords : Airborne asbestos, ELCR (Excess Lifetime Cancer Risk), Health risk assessment, Slate roofing house