Abstract： Objective To investigate gene expression of three nitric oxide synthase isozymes in injure d spinal cord tissue. Methods Thirty-six adult SD rats were randomly divided into six groups: a normal group and five injury groups, with six per each group. Animals in the injury groups w ere sacrificed at 2, 6, 12, 24, 48 h after injury. A compression injury model o n the spinal cord was made according to Nystrom B et al and gene expression of t he three NOS isozymes were examined by reverse transcription polymerase chain re action (RT-PCR). Results Gene expression of nNOS and eNOS were detectable in the normal group and were up -regulated quickly after injury, reaching a maximum at 6 h: (0.633±0.012) a nd (1.236±0.207). Gene expression of iNOS was detectable only in the injur y groups and it was gradually up-regulated after injury, reaching a maximum at 24 h:(1.043±0.049).Conclusion Injury to the spinal cord leads to early up-regulation of cNOS and late up-reg ulation of iNOS. Different NOS isozymes may play different roles in secondary s pinal cord injury.