Surface ozone(O-3) was measured at Oki Island(Japan), Cheju Island(South Korea), Lanyu Island(Taiwan Province, China), Cape D’Aguilar(Hong Kong SAR) and Lin’an, Longfenshan, Waliguan(China mainland) during January 1994—December 1996 as a component of IGAC/APARE(International Global Atmospheric Chemistry/East Asia-North Pacific Regional Experiment). This paper gave a joint discussion on the observational results at these stations over the study region. Investigations showed that the average of surface O 3 mixing ratios at the seven sites are 47.9±15.8, 48.1±17.9, 30.2±16.4, 31.6±17.5, 36.3±17.5, 34.8±11.5 and 48.2±9.5 ppbv, respectively. Significant diurnal variations of surface O 3 have been observed at Oki, Cheju, D’Aguilar, Lin’an and Longfenshan. Their annual averaged diurnal differences range from 8 to 23 ppbv and differ in each season. Surface O 3 at Lanyu and Waliguan do not show strong diurnal variability. Seasonal cycles of surface O 3 showed difference at the temperate and the subtropical remote sites. Oki has a summer minimum-spring maximum, while Lanyu has a summer minimum-autumn maximum. The suburban sites at D’Aguilar and Lin’an report high-level O 3 in autumn and low level O 3 in summer. Surface O 3 remains high in autumn and low in winter at the rural site Longfenshan. For the global background station Waliguan, surface O 3 exhibits a broad spring-summer maximum and autumn-winter minimum. The backward air trajectories to these sites have shown different pathways of long-range transport of air pollution from East Asia Continent to North Pacific Ocean. Surface O 3 was found to be strongly and positively correlated with CO at Oki and Lanyu, especially in spring and autumn, reflecting the substantial photochemical buildup of O-3 on a regional scale. It is believed that the regional sources of pollution in East Asia have enhanced the average surface O 3 concentrations in the background atmosphere of North Pacific. Surface Ozone (O - 3) was measured at Oki Island (Japan), Cheju Island (South Korea), Lanyu Island (Taiwan Province, China), Cape D’Aguilar (Hong Kong SAR) and Lin’an, Longfenshan, Waliguan (China mainland) during January 1994-December 1996 as a component of IGAC / APARE (International Global Atmospheric Chemistry / East Asia-North Pacific Regional Experiment). This paper gave a joint discussion on the observational results at these stations over the study region . Investigations showed that the average of surface O 3 mixing ratios at the seven sites are 47.9 ± 15.8, 48.1 ± 17.9, 30.2 ± 16.4, 31.6 ± 17.5, 36.3 ± 17.5, 34.8 ± 11.5 and 48.2 ± 9.5 ppbv, respectively. Significant diurnal variations of surface O 3 have been observed at Oki, Cheju, D’Aguilar, Lin’an and Longfenshan. Their annual averaged diurnal differences range from 8 to 23 ppbv and differ in each season. Surface O 3 at Lanyu and Waliguan do not show Strong diurnal variability. Seasonal cycles of surface O 3 showed difference at the temperate and the subtropical remote sites. Oki has a summer minimum-spring maximum, while Lanyu has a summer minimum-autumn maximum. The suburban sites at D’Aguilar and Lin’an report high-level O 3 in autumn and low level O 3 in the summer. Surface O 3 remains high in autumn and low in winter at the rural site Longfenshan. For the global background station Waliguan, surface O 3 exhibits a broad spring-summer maximum and autumn-winter minimum. The backward air trajectories to these sites have shown different pathways of long-range transport of air pollution from East Asia Continent to North Pacific Ocean. Surface O 3 was found to be strongly and positively correlated with CO at Oki and Lanyu, especially in spring and autumn, reflecting the substantial photochemical buildup of O - 3 on a regional scale. It is believed that the regional sources of pollution in East Asia have enhanced the average surface O 3 concentrations in the background atmosphere of North Pacific.