Soil salinity is a major abiotic stress that lowers agricultural production around the world. Mainly caused by elevated levels of NaCl, it induces a wide range of responses in plants. In addition to ion toxicity, high salt levels can induce oxidative stress with the formation and accumulation of reactive oxygen species (ROS). We introduced the transcription factor YAP1, originally from yeast (Saccharomyces cerevisiae), into Arabidopsis thaliana (ecotype Columbia). When treated with various NaC1 concentrations, transgenic plants showed increased activities of antioxidant enzymes catalase, superoxide dismutase, ascorbate peroxidase, peroxidase, glutathione S-transferase, and glutathione reductase compared with the wild-type Arabidopsis. This demonstrated that an active oxygen scavenging system was enhanced to protect plants from salt stress by equilibrating ROS metabolism. Transgenic Arabidopsis maintained higher photosynthesis levels and lower amounts of $H_{2}O_{2}$, suggesting that ROS production was reduced. Physiological analysis implied that transgenic Arabidopsis might employ multiple mechanisms to improve its salt tolerance.