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Drought is a critical abiotic stress which leads to crop yield and a decrease in quality. Annexins belong to a multi-gene family of calcium- and lipid-binding proteins and play diverse roles in plant growth and development. Herein, we report a rice annexin protein, OsANN9, which in addition to regular annexin repeats and type-II Ca²⁺ binding sites, also consists of a C2H2-type zinc-finger domain. We found that the expression of <i>OsANN9</i> was upregulated by polyethylene glycol (PEG) or water-deficient treatment. Moreover, plants that overexpressed <i>OsANN9</i> had increased survival rates under drought stress, while both <i>OsANN9</i>-RNAi and <i>osann9</i> mutants showed sensitivity to drought. In addition, the overexpression of <i>OsANN9</i> increased superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities, which regulate reactive oxygen species homeostasis. Collectively, these findings indicate that OsANN9 may function as a positive regulator in response to drought stress by modulating antioxidant accumulation. Interestingly, the setting rates of <i>osann9</i> mutant rice plants significantly decreased in comparison to wild-type plants, suggesting that OsANN9 might be involved in other molecular mechanisms in the rice seed development stage.