This study investigates the influences of diurnal variations on the summer time monsoonal precipitation over Asia . To this end, two sets of experiments are designed in a regional climate modeling framework forced laterally by the reanalysis data. The year of 2004 was chosen, which is characterized by a near-normal summer precipitation in Asia. The control experiment is a normal integration in which radiation is computed hourly, whereas in the no-diurnal experiment the daily averaged solar flux is used and the radiation is computed once a day. The analysis of the results from the two experiments revealed that the reduction of seasonal precipitation is evident in the case of the no-diurnal experiment, as compared to the control run but with a more uniform response over the oceans than over land, i.e., in some areas over land, precipitation increase when the diurnal variation is removed. The diurnal variation of atmosphere and land do not affect the overall distribution of monsoonal precipitation. Over land, the precipitation has marked diurnal variation in the control but not in the non-diurnal run and daily average is reflected by the amplitude of the diurnal variation. The resulting impact is found to be more complicated in the Indian monsoon than in the East Asian monsoon. The physical and dynamical mechanisms of the difference in precipitation between the two experiments will be analyzed in detail and presented.