Surface pCO2, temperature, salinity, nutrients, and chlorophyll a were measured in the East China Sea (31~34 °N, 124~128 °E) from August 26 to September 2, 2003, and from April 28 to May 7, 2004. The high-salinity Tsushima Warm Current was observed in the east of the survey area in both years. Consequently, temperature and salinity showed similar distributions in the summer of 2003 and the spring of 2004. By contrast, the surface pCO2 changed dramatically from summer to spring across the shelf front, where the Tsushima Warm Current meets Yellow Sea water. High pCO2 (> 380 μatm) in the east, and low pCO2 (< 280 μatm) in the west, off China, were observed in the summer of 2003, and the pattern was reversed in the spring of 2004. Surface pCO2 was positively correlated with temperature in the east of the shelf front in both summer and spring (r=0.82 and 0.74, respectively). Therefore, east of the front, temperature is thought to control surface pCO2 primarily, while west of the front it is controlled by many factors, such as fresh water discharge from Yangtze River in summer, water stability, primary productivity, and organic decomposition. The highly elevated pCO2 west of the front in spring despite the low temperature and high chlorophyll concentration might be the result of surface water mixing with CO2-rich bottom waters in spring or massive fresh water discharge from the Yangtze River in summer.