Mesolows in the Taiwan Mei-Yu seasons of 1983-1987 were analyzed for each 0.5 × 0.5 degree latitude-longitude grid square using 6 hourly surface observations. Spatial and temporal distribution of the mesolow frequency was investigated. The intensity and its diurnal variation were studied.It was found that the mesolows tended to form over the area to the southeast, northwest and southwest of Taiwan. The mean life time was about 15.5 h and it was longer over the eastern side of the Central Mountain Range than over the western side. The mean intensity of mesolow was stronger over the ocean as compared to that over the land was stronger over the eastern side than over the western side. The formation and the diurnal variation of mesolow appeared to be affected by the semi-diurnal pressure wave. The strong mesolow were affected to a lesser degree than the weaker ones.