Abstract: A gene encoding a superoxide dismutase was isolated from senescent leave of cotton(Gossypium hirsutum) cv CRI36 by utilizing rapid amplification of cDNA ends polymerase chain reaction(RACE-PCR),and set of consensus oligonucleotide primers was designed to anneal the conserved sequences of plant Cu/Zn SOD genes. the cDNA ,which designated Cu/Zn-SOD gene,contained 682 bp terminating in a poly(A)+signal. and the opening reading frame (ORF)456bp encodes polypeptide 152 amino acid with the predicted molecular mass of 15.03 Kd and theoretical Pi of6.09.A comparison of the deduced amino sequence with the sequence in the Genbank database has shown considerable sequence similarity to a family of plant Cu/Zn SOD. This putative cotton Cu/Zn SOD shows from 82% to 87% identity to the other plants. All of them share catalytic tetrad of residues, which are highly conserved in four redions. A characteristic feature of Cu/Zn SOD is the inexistence of the signal peptide at the N-terminal region. that suggests the Cu/Zn SOD localizes to the cytoplasm. the Cu/Zn SOD is encoded by nucleolus gene, southern blotting shown that gene had different copies in different cotton cultivars ; only one copy in upland cotton .the expression of the Cu/Zn SOD gene was determined using northern blotting analysis. the Cu/Zn SOD mRNA levels show regular changing in the total development stages：lower in prophase, higher in upper stage and highest at the opening flower stage. the curve of the Cu/Zn SOD mRNA levels is consistent with that of Cu/Zn SOD enzyme activity. the Cu/Zn SOD mRNA levels of different organs shows that the gene are higher in the root, next lesf, lower in the flower.