The Japan Meteorological Agency (JMA) used ERS-2 scatterometer winds and surface pressure retrieved from the ERS-2 winds together with auxiliary data to assimilate them operationally in the optimum interpolation scheme (OI) from July 1998 to January 2001. The QuikSCAT satellite, a successor of ERS-2, was launched being equipped with a new scatterometer SeaWinds in June 1999. A large contribution to numerical weather prediction (NWP) is expected, as the width of QuikSCAT observation is more than three times wider than that of ERS-2 scatterometer. Taking an advantage of QuikSCAT winds, an observation system experiment (OSE) for QuikSCAT winds in July 2000 was conducted with the same assimilation method as that used for ERS-2 data. Results showed that QuikSCAT winds after the ambiguity removal and quality control performed at JMA had almost the same accuracy as ship or buoy data. JMA introduced a three-dimensional variational scheme (3D-VAR) instead of OI to the global data assimilation system in September 2001. Using QuikSCAT winds in July 2000, an impact study was performed with the JMA 3D-VAR using T106L40 version of the JMA global NWP model. The results showed a large improvement over the Southern Hemisphere and a small or a neutral improvement over the Tropics and the Northern Hemisphere. To use QuikSCAT Winds operationally with the JMA 3D-VAR, an impact study using QuikSCAT winds in December 2001 is performed with the T213L40 version of the JMA global NWP model, and results are presented at the meeting. It is scheduled to introduce QuikSCAT Winds in operation to the T213L40 version of the JMA global NWP model by the end of this year at the latest.