The sleep-wake cycle is an organism-level physiological phenomenon conserved in a wide range of species, however, the molecular mechanisms remain largely unexplored. We have previously shown that Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), one of the protein kinases regulated by intracellular Ca²⁺, plays a critical role in promoting sleep (Tatsuki et al, 2016). CaMKII function is precisely controlled by phosphorylation in response to neural activity, suggesting that transitions of the CaMKII phosphorylation states are deeply involved in driving the sleep-wake cycle. In this study, we comprehensively analyzed the effects of CaMKII phosphomimetic mutations on sleep phenotypes in mice. We found that the phosphorylation of a single residue in CaMKII could induce sleep from wakefulness. We further revealed that additional phosphorylation switches the CaMKII function from sleep induction to sleep maintenance. These results provide evidence that CaMKII plays multiple roles in sleep-wake regulation, depending on its phosphorylation state.