Recently, the high PCDD/F emissions observed in the coastal provinces of eastern China have raised global concerns over their adverse effects on human health. To address the effects of the long-range transport of persistent organic pollutants, the observations of atmospheric PCDD/F pollution were conducted across Southeast Asian in this study. Atmospheric PCDD/F levels were evaluated at two background stations (Sites A and B) in Taiwan, three remote islands (Sites C, D and E) around Taiwan and at Dongsha Island (Site F) in South China Sea at various times. Significantly lower atmospheric PCDD/F concentrations (1.24-7.75fg I-TEQm-3) and PCDD/F contents (3.45-49.1pg I-TEQ/g-TSP) in total suspended particles (TSPs) were measured during the summer season. Based on a 72-h backward trajectory analysis conducted for the sampling sites used in this study, the air mass containing theses low levels had originated from the Pacific Ocean and South China Sea during the summer. The highest PCDD/F concentrations (10.2-65.2fgI-TEQm-3) and PCDD/F contents (132-620pg I-TEQ/g-TSP) in ambient air were measured in northern Taiwan (Site A) and at two islands (Site C and Site E) close to mainland China during the northeast monsoon periods. In the meantime, the PCDF compounds in ambient air also increased from 52-54% to 65-75% at those sampling sites. Based on these measurements and corresponding trajectory analysis, we conclude that the significant increase in atmospheric PCDD/Fs measured during the northeast monsoon period in this study was attributable to the long-range transport of emissions from the coastal regions of mainland China.