Based on the 6-hourly weather observations at 71 stations across the central and eastern Tibetan Plateau (TP) during 1961--2003, the change of cloud amount and its possible connection with recent climate warming on TP were investigated. The low-level cloud amount exhibits a significant increasing trend during the nighttimes, leading to the enhanced atmospheric counterradiation, weakened effective terrestrial radiation, and the subsequently strong nocturnal surface warming. On the other hand, both the total and low-level cloud amounts during daytime display decreasing trends, resulting in more absorbing of direct solar radiation at the surface and the associated surface warming. Since the increase in nocturnal low-level cloud is more than the decrease of daytime low and total cloud amounts, such changes in cloud amount contribute to at least partly of the increased surface air temperature and its diminished diurnal range on TP.