Subclass Ⅲ sucrose nonfermenting1-related protein kinase 2s (SnRK2s) function in ABA and abiotic stress responses by unknown mechanisms. We found that osmotic stress/ABA-activated protein kinase 10 (SAPK10), a member of rice SnRK2s, physically interacted with CBL-interacting protein kinase 1 (OsCIPK1). OsCIPK1 expression was up-regulated by ABA and PEG treatment, and overexpression increased the ABA sensitivity of seed germination and root growth and plant osmotic stress tolerance. Osmotic stress or ABA-induced activation of OsCIPK1 is dependent on SAPK10. SAPK10 phosphorylates Thr-24 of OsCIPK1 in vitro, and this phosphorylation increases the activity of OsCIPK1 and positively regulates the function of OsCIPK1 in ABA responses and plant osmotic stress tolerance. This study suggests that OsCIPK1 is a direct phosphorylated substrate of SAPK10, and SAPK10-mediated phosphorylation of OsCIPK1 functions in ABA signaling and increases rice osmotic stress tolerance.