Red blood cell is a small subunit encoding 1, 5-ribulose bisphosphate carboxylase/ oxygenase (Rubisco). It could control the catalytic activity of Rubisco and play an important role in plant photosynthesis. , a small subunit of Rubisco, is cloned from . It has a strong low-temperature photosynthetic and photorespiration ability, but its mechanism in cold tolerance remains to be unknown. The results of quantitative PCR showed that gene could be induced by low-temperature, osmosis, and salt stress. Its expression was increased with the decrease of temperature, which was consistent with the habitat of . Overexpression of could significantly increase the mRNA expressions of SlrbcL and SlRCA in transgenic tomato seedlings. Furthermore, the activity and content of Rubisco and Rubisco activase (RCA) in transgenic tomato seedlings were also significantly higher than those in wild-type plants. The contents of chlorophyll and carotenoids, soluble sugar, and starch in the leaves of transgenic plants were significantly higher than those in WT plants, as well as the plant height, leaf area, and dry matter weight. Moreover, compared with WT, MDA content was decreased, and activities of SOD, POD, CAT, and APX were significantly higher in transgenic lines. In conclusion, our results suggested that overexpression of can reduce the damage of low temperature on photosynthesis of tomato seedlings. It could help achieve relatively stable photosynthesis, enhance scavenging ROS ability of tomato seedlings, maintain stable membrane structure, and improve cold tolerance of tomato.