The predictability of high temperatures is important for intertidal species for coping with thermal stress. To investigate the roles of high temperature and its predictability on the population abundance and reproductive output of an intertidal rocky shore limpet, Siphonaria japonica, we monitored the operative temperature, recorded the population abundance of egg ribbons and adults, and quantified the expression of heat shock protein 70 ( hsp70) mRNA on two warm-temperate rocky shores with different thermal environments. Abundances of limpets and egg ribbons in the hotter but more predictable (HP) habitats were higher than those in the relatively benign and unpredictable (BU) habitats. In the HP habitats, there was a strong positive correlation between habitat temperature and population abundance. For limpets living in the HP habitats, the expression of hsp70 exhibited a smaller increase with rising body temperature than for BU limpets, indicating the existence in HP limpets of a preparatory strategy in cellular stress response against thermal stress. Our results demonstrate that the predictability of operative temperature can affect physiological responses and population dynamics. The importance of predictability should be considered in analyses of the ecological consequences of climate warming.