The temporal-spatial distribution of thin moist layers in the midtroposphere over the tropical eastern Pacific is studied by data analyses of radiosonde soundings and downscaling numerical experiments with a regional model. The downscaling experiments with global objective analyses are completed for 2005-06, September and December of 1999-2004, and March of 2000-04. The vertical distribution of thin moist layers has three local maxima at 5, 10, and 16 km, where bimodality of the frequency distribution of water vapor is evident. Between 4 and 7 km, an annual variation is dominant in the occurrence ratio of thin moist layers, which tend to appear in nonconvective regions. In boreal winter, the layers appear to the north of the intertropical convergence zone (ITCZ), whereas in boreal summer the layers appear in the equator-side of the ITCZ.