This study attempts to investigate size distribution of particulate matters emitted from medical waste burning and ambient air quality of a hopistal in a remote area of Cambodia. The particulate matters are mainly discussed in different size ranges of 0.1-10 µm, which was sampled by a nano-sampler on a single chamber incinerator (SCI) and a stella incinerator (SI). In addition, carbonaceous aerosols and gaseous pollutants were also included. The results show that SCI produced carbonaceous aerosols and gaseous pollutants significantly higher than SI while the pollutants in the surrounding areas were naturally diluted by the ambient air. The median mass aerodynamic diameters (MMAD) of the surrounding area are 0.8 µm for SI and 1.0 µm for SCI. Total suspended particle emission by SCI (714.4 µg/m3) is 11.5 folds greater than that by SI (62.5 µg/m3). Furthermore, the fine particles, PM2.5, were as high as the nano particles PM0.1 around 20-25% from both incinerators and the surrounding areas (approximately 80-180 m in distants). The high concentration of particulate matters released from both incinerators might influence the ambient air quality, which was very awful impact to the local people, patients, and staffs in the hospital.