This study examines the effects of heavy rainfall on the Kuroshio surface salinity east of Taiwan. The main focus of this study is on the abnormal hydrologic characteristics of the Kuroshio after heavy rainfall. Data of sea surface salinity (SSS) are derived from R/V Ocean Researcher I (R/V OR1) 1012 cruise and 8 glider cruises; data of rain rate from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) which helps to figure out the change of SSS of the Kuroshio from field surveys and glider datasets. The results show a good correlation between the rain rate and minimum SSS with a coefficient of determination of 0.74. The rainfall causes the SSS of the Kuroshio surface water drops 0.176 psu per 1 mm/hr rain rate. This underscore the importance of hydrologic characteristic fluctuations must be taken into account for seasonal or long-term variability study.