Cadmium (Cd) pollution threatens global food security and many plant growth regulators have been found to improve plant Cd resistance. Jasmonate, a low molecular-weight plant growth regulator, is involved in the processes by which plants respond to Cd stress. However, the underlying mechanisms involved in these processes are unclear. In the present study, we investigated the effects of methyl jasmonate (MeJA, a jasmonate active substance) on maize seedling growth under Cd stress conditions. We found that exogenous MeJA induced the accumulation of polyamines (PAs), especially spermidine (spd), and exogenous MeJA application partially mitigated the Cd-induced inhibition of whole-plant growth. Under Cd stress, the MeJAand spd-treated plant leaves contained less Cd than the leaves of plants not treated with MeJA or spd. With the addition of the spd synthesis inhibitor dicyclohexylamine and MeJA under Cd stress conditions, the leaf Cd concentration was higher than that under the Cd treatment alone, and the JA-induced improvement in maize Cd resistance was eliminated. This suggests that spermidine plays an important role in JA-induced improved Cd resistance in maize seedlings by repressing Cd transport from roots to leaves.