Leaf early senescence can directly reduce photosynthesis and crop yield. Unlocking the mechanism of leaf early senescence becomes important via building up the strategy to achieve high and stable rice yield. A water-soaked spot mutant (termed wss1) was identified in the population derived from EMS-treated seeds of the indica rice variety JG30. At the tillering stage, the leaves of wss1 showed premature senescence, including the appearance of water-soaked spots, which further developed to the leaf necrosis. In relative to the parental line JG30, wss1 mutant showed 30%, 22% and 50% reduction on the plant height, seed setting rate and number of grains per panicle, respectively. The chlorophyll content in the water-soaked spot leaves of wss1 was significantly lower than that of the wild-type plants. By trypan blue cell histochemical staining, the cell membrane of wss1 on leaves was destroyed. Genetic analysis showed that wss1 was controlled by a recessive gene (wss1), which was mapped in a 1200 kb region between markers Ch11-33 and Ch11-123. Thus, these results will benefit future molecular cloning and functional characterization of the underlying gene of Oswss1.