Peatland fires predominantly occur on Sumatra and Kalimantan islands in Indonesia during every dry season. Smoke aerosols generated from these fires travel to other countries, resulting in serious transboundary haze pollution in Southeast Asia. Specifically, the western coast of the Malay Peninsula, located downwind of Sumatra Island during the dry season, is highly susceptible to the influence of Indonesian peatland fires. For more than a decade, beginning from the author’s academic years, collaborative research initiatives mainly with Indonesia and Malaysia have been conducted to observe atmospheric aerosols, primarily PM_2.5, in the peatland fire source regions of Riau Province, Sumatra in Indonesia, and the receptor sites in Malaysia. This paper provides an overview of the chemical characteristics of particulate matter at Indonesian peatland fire sources and receptor sites in Malaysia, based on the author’s observational results. Additionally, future research directions are discussed.