Abstract: This study investigated the change of antioxidant enzymes (including SOD, CAT and POD), proline content, MDA and reactive oxygen species (ROS) in horsebean seedlings under Cd stress, and to study the protective effect of NO and H₂O₂. Sodium nitro presside (SNP) was used as a NO donor. Application of SNP and H₂O₂, alone and in mixtures helped protect horsebean seedling leaves from Cd oxidative damage. However, treatment E showed a much better protective impact than treatments C and D, which significantly increased activities of antioxidant enzymes. Seventy two hours after Cd stress, SOD reached its maximum (57.89% over the control). Forty eight hours after Cd stress, the activities of CAT and POD reached a maximum (69.60% and 101.18% over the control). One hundred and twenty hours after Cd stress, the proline content in treatment E increased by 134.88% compared with treatment B, and the contents of MDA, and H₂O₂ were largely reduced as was the production rate of O₂^·-.