By using MODIS/SSMI merged water vapor data, the evolution of total precipitable water (TPW) associated with the Asian and Australian monsoons has been studied. In addition to the satellite data, the monthly means of TPW data from the National Center for Environmental Prediction (NCEP) Reanalysis II and the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-year Reanalysis (ERA-40) are used to compare with the merged TPW data. The large TPW is associated with the onsets of the Asian and Australian monsoons and shows a pronounced seasonal variability. Within northern Australia the annual mean TPW from the NCEP and SSMI/MODIS data sets show a decreasing trend over the last five years and the ERA-40 over the 2.5 years but no obvious trend can be found within southern Asia, indicating that the atmosphere tends to become drier over the Australian monsoon region. The result from available ERA-40 data set shows a quite similar feature with that of the merged TPW. However the NCEP TPW, which may be mostly influenced by the forecast model, particularly, by the performance of the physical parameterizations, has underestimated the TPW and has a rather unsystematic evolution in terms of seasonal migration.