Water is the most important factor for plant growth, and deficiency of water is a reason for drought stress. In drought stress situations, antioxidant system and some biochemical properties are changed. To identify the effect of drought stress on some types of citrus species, we examined different irrigation periods on citrus cultivars. In this study, plants were irrigated every four, eight, twelve, and sixteen days. Antioxidant, superoxide dismutase (SOD), peroxidase (POD), chlorophyll content, relative water content (RWC), and proline were measured. Results showed that with increased irrigation period antioxidant capacity, SOD, POD, and proline were increased in all three citrus cultivars, but chlorophyll content and RWC were decreased. All cultivars expressed similar changing pattern and it means that with decrease of water availability antioxidant system activity increases to protect plants against drought stress