In this paper, precipitable water vapor (PWV) values calculated from MODIS satellite data are compared to the PWV values calculated from GPS data. Analysis of one-year data from 9 stations, shows that the MODIS derived PWV values correlate well with the GPS PWV values with the correlation coefcients of 0.85, 0.94 and 0.85 for tropical, sub-tropical and temperate regions respectively under the clear sky conditions. The average root mean square (RMS) error for clear sky conditions were calculated to be 7.80 mm, 5.47 mm and 4.19 mm for tropical, sub-tropical and temperate regions respectively. It was found that, generally MODIS overestimates the PWV values especially in regions with higher water vapor content.