Superoxide dismutase (SOD) plays an important role in the stress tolerance of higher plants. In the present study, a novel Cu/Zn-SOD gene, SiCSD (accession no. KC912564), was cloned from Saussurea involucrata Kar. & Kir. The deduced amino acid sequence shared 85% identity with Cu/Zn-SOD of Solanum tuberosum L. and Solanum lycopersicum L. Quantitative real-time polymerase chain reaction showed that SiCSD was upregulated by treatments with cold, drought, and oxidative stresses. SiCSD transgenic tobacco plants improved tolerance to drought, freezing, and oxidative stresses and exhibited a higher survival rate, relative water content, photosynthesis efficiency, and higher activities of SODs, catalases, and ascorbate peroxidase, but lower ion leakage and malondialdehyde contents compared with the wild type. These data demonstrate that SiCSD may act as a positive regulator in drought and cold stress by reducing oxidant injury.