Abstract: Source relationships were calculated for surface sulfur oxide (SO_2+sulphate) concentrations in East Asia using the CAMx model with Particulate Matter Source Apportionment Technology (PSAT). The domain was divided into 43 source regions including 33 source regions in China. Three regions in the Japanese main islands (northern, central, and southern Japan), as well as the Korean peninsula and Cheju Island of Korea and the Okinawa islands of Japan were set as receptors. The greatest contributions to the sulfur oxides in the northern, central, and southern parts of Japan were emissions from Japan itself, accounting for 73.8%, 77.1% and 65.9% respectively, while the second greatest contributions to sulfur oxides in the three receptors were emissions from China, supplying 23.5%, 20.2% and 25.8%, respectively. As for Korea, 67.8% of the sulfur oxides in the Korean peninsula originated from Korea and 27.2% from China. For Cheju and Okinawa islands, the sulfur oxide sources were different from other areas in Korea and Japan. The seasonal variations of trans-boundary sulfur oxide pollution contribution in the receptors varied from the north to the south. The greatest contribution of trans-boundary sulfur oxide pollution in Korea and southern Japan occurred in January, while the lowest contribution happened in July. In northern and central Japan, the greatest contribution occurred in April, while the lowest happened in January. The concentrations of trans-boundary sulfur oxide pollution in Japan and Korea were low:less than 1.5 μg/m³ in Japan and less than 2.5 μg/m³ in the Korean peninsula. Among Chinese source regions, Shandong, Hebei, Jiangsu and Liaoning were the main sources contributing to sulfur oxides in Japan and Korea. The spatial distribution of sulfur oxide horizontal transport flux at low altitude well matched the source-receptor relationships.