In this study, five different concentrations (50, 100, 150, 200, 250 μmol/L) of melatonin (MT) were sprayed to the eggplant seedlings under the stress of low light and low temperature, CK and CK1 were sprayed with fresh water but the CK was under natural light and CK1 was under the stress of low light and low temperature, to study the effects of different concentrations of MT on the physiological characteristics of eggplant seedlings under the stress of low light and low temperature. The results showed that photosynthetic pigment content, PSII photochemistry, and efficiency of light energy conversion and rate of photosynthesis in eggplant seedling kept at high level when the concentration of melatonin was below 200 μmol/L; when the MT concentration was 150 μmol/L, the total chlorophyll and carotenoid content of eggplant were 40.23% and 75.00% higher respectively than those of CK1; the activities of antioxidase (POD,SOD,CAT) increased significantly and the POD activity was 108.66% higher than CK1; the accumulations of proline and soluble sugar were accelerated and the soluble sugar content was 50.61% higher than CK1, while the content of malonaldehyde was reduced in leaves of eggplant seedling. Thus, exogenous melatonin can enhance the resistance to the stress of low light and low temperature of eggplant seedling, and the best concentration is 150 μmol/L.