The upper tropospheric water vapor (UTWV) from the reanalysis produced by the Goddard Earth Observing System (GEOS) Data Assimilation System is compared with the retrieved UTWV from the measurements of the Microwave Limb Sounder (MLS) aboard the Upper Atmosphere Research Satellite (UARS). The UTWV from the GEOS reanalysis is in fair agreement with the UTWV retrieved from the UARS MLS observation. Both data sets show high tropical UTWV closely related with the tropical deep convection. There is, however, clear evidence of overestimation of UTWV in the GEOS reanalysis, especially for the summer season (July 1992). The GEOS overestimation is more significant after considering the MLS retrieval bias. The reasons for the GEOS overestimation are discussed. For interannual variations between 1992 and 1993, the reanalysis and the observation consistently show significant changes in UTWV resulting from sea surface temperature anomalies associated with the El Ni¿o-Southern Oscillation phenomenon. ¿ 1998 American Geophysical Union