In this study, a gene encoding a superoxide dismutase (SOD) was cloned from senescent leaves of cotton (Gossypium hirsutum), and its expressing profile was analyzed. The gene was cloned by rapid amplification of cDNA ends (RACE)method. Northern blotting was used to show the profile of the gene expression, and the enzyme activity was mensurated by NBT deoxidization method in different growth periods. The full length of a gene of cytosolic copper/zinc superoxide dismutase (Cu/Zn-SOD) was isolated from cotton (GenBank Accession Number: DQ445093). The sequence of cDNA contained 682 bp, the opening reading frame 456 bp, and encoded polypeptide 152 amino acids with the predicted molecular mass of 15.03 kD and theoretical pI of 6.09. The amino acid sequence was similar with the other plants from 82 to 87%. Southern blotting showed that the gene had different number of copies in different cotton species. Northern blotting suggested that the gene had different expression in different tissues and development stages. The enzyme activity was the highest in peak flowering stage. The cotton cytosolic (Cu/Zn-SOD) had lower copies in the upland cotton. The copper/zinc superoxide dismutase mRNA expressing level showed regular changing in the whole development stages; it was lower in the former stages, higher in latter stages and the highest at the peak flowering stage. The curve of the copper/zinc superoxide dismutase mRNA expressing level was consistent with that of the Cu/Zn-SOD enzyme activity.The copper/zinc superoxide dismutase mRNA expressing levels of different organs showed that the gene was higher in the root, leaf, and lower in the flower.