Abstract: Short-term effects of elevated seawater pCO₂ concentration on phytoplankton community structure were examined from a controlled 10-d incubation experiment onboard in a nearshore area in Rongcheng Bay, Yellow Sea, China.The control treatments were bubbled with ambient air (395 ppm CO₂) and the experimental treatments were set in 1000 ppm CO₂ (future scenario of the year 2100).Results showed that chlorophyll a concentration and phytoplankton abundance increased and species diversity decreased in CO₂ treatments than that in control treatments.Abundance of Nitzschia spp.and Guinardia striata increased obviously in CO₂ treatments.Simultaneously, abundance of Thalassiosira spp.and Skeletonema costatum changed insignificantly between two treatments.Our research showed that ocean acidification altered phytoplankton community structure and impacted phytoplankton assemblage succession in nearshore of Yellow Sea.More research should be conducted to investigate influence of ocean acidification on marine ecosystem.