Abstract: A study has been undertaken to explore the effect of cadmium (Cd²⁺) on Cosmos bipinnatus seed germination and to discover the optimal treatment mode and concentration of exogenous methyl jasmonate (MeJA) under Cd²⁺ stress. Seeds were germinated on filter paper bedding and measurements taken of germination potential, germination rate, vigor index, plumule lengths, fresh weights, malonic dialdehyde (MDA) and the activity of antioxidant enzymes. The results showed that germination potential, germination rate, vigor index and plumule length reduced gradually with increases in Cd²⁺ concentration. C. bipinnatus seeds can endure low Cd²⁺ concentrations (<0.6 mmol/L), but their germination indexes were significantly inhibited by high concentrations (≥0.6 mmol/L). The performance of seeds pretreated with MeJA was higher than that of seeds subjected to Cd²⁺ and MeJA simultaneously. The optimal treatment concentration was 1.0 μmol/L MeJA which, compared to treatment with Cd²⁺ only, increased germination rate by 19.3%, vigor index by 73.0%, fresh weight by 28.1% and reduced MDA contents. The alleviation effect of low concentrations of MeJA on seed germination under Cd²⁺ stress was mainly through increasing peroxidase, catalase and glutathione reductase activity to scavenge reactive oxygen species and reduce lipid peroxidation of the membrane.