Abstract. In this paper, the performances of two operational ocean forecasting systems, Mercator Océan (MO) in France and South China Sea Operational Forecasting System (SCSOFS) in China, have been examined. Both systems can provide science-based nowcast/forecast products, such as temperature, salinity, water level and ocean circulations. Based on the observed satellite and in-situ data have been obtained in 2012 in the South China Sea, the comparison and validation of the ocean circulations, the structures of the temperature and salinity, and some mesoscale activities are shown. Comparing with the observation, the ocean circulations and SST of MO show better results than those of SCSOFS. However, the structures of temperature and salinity of SCSOFS are better than those of MO. For the mesoscale activities, SST fronts and SST decreasing during the typhoon Tembin of SCSOFS are better agreement with the previous study or satellite data than those of MO; but both of them show some differences from AVISO data. Finally, according to the results compared in above, some suggestions have been proposed for both systems to improve their performances in the near further.