We systematically evaluated the impact of GPSRO data on typhoon track prediction over the Northwestern Pacific during 2008 to 2010. Specifically, we perform data assimilation and forecast experiments using the TWRF system at 45km resolution on 11 typhoons, with or without the use of GPSRO refractivity. The results indicate that the assimilation of GPSRO reduces the 72-hour track forecast errors by ~12km (5 %). Although this is only a modest improvement, it is statistically significant.