The study investigates the use of chemical pesticide and its impact on health and other problems of Hmong and Karen ethnic groups residing in the Klang River Basin in the Inthanon National Park, Tambon Ban Luang, Chom Thong District, Chiang Mai Province. The sample group consisted of 180 households from a total of 280 households in the study area. The study finding revealed that some used the chemicals according to instructions on the labels, while others used them according to their own approximation. It was further found that their practices were not correct and safe, such as not wearing hats, gloves, shoes, or preventive masks. In terms of health effects, the sample group experienced health problems, for instance, dizziness, nausea, and skin irritation. Additionally, they devised their own use of the chemicals by increasing the quantity per rai. They had no knowledge on safety, were careless and lacked conscience on safety of consumers.