Resveratrol is a natural polyphenol derived mainly from the skin of grapes and from red wine. Resveratrol prolongs life span in several invertebrates, but this function is not found in mice. Our recently published paper demonstrated that resveratrol prolonged longevity of the annual fish Nothobranchius guentheri, a promising vertebrate model for anti-aging research. However, the anti-aging process by resveratrol remains largely unexplored, and little is known about its effects on oxidative stress. In this study, by long-term supplementation of resveratrol from sexual maturity onward in the annual fish, we detected survivorship and oxidative stress at three different developmental stages in vivo. A total of 112 fish were fed with resveratrol in the concentration of 200 μg/gram food and 111 fish without resveratrol from 16 weeks of age until to the end of their lives. The mean and maximum life spans of the fish treated with resveratrol were extended by 17.34% and 17.66%, respectively, compared to the fish in control group. The markers of oxidative stress, such as the levels of reactive oxygen species (ROS), the activities of anti-oxidant enzymes, and the degree of oxidative damage, were detected at 6, 9, and 12 months, respectively. The results showed that levels of ROS and oxidative damage increased and activities of anti-oxidant enzymes appeared to decrease with age. Resveratrol treatment significantly attenuated the increase of ROS and oxidative damage and up-regulated the decrease of anti-oxidant enzyme activities induced by aging. Our results demonstrated that resveratrol decreased oxidative stress and extended life span in this short-lived fish.