Amaranthin is one of the important plant secondary metabolites. Light can trigger the initiation of amaranthin biosynthesis in cotyledons of Amaranthus mangostanus~20 mg/L) induced amaranthin accumulation was dose-dependent both in light and darkness. When in darkness, 20 mg/L MeJA induced 10.91–fold amaranthin contents that of controls. While in light, presence of 20 mg/L MeJA induced 2.23-fold that of cotyledons exposed to light only. When used 4-leaf stage seedlings as material, MeJA (1.25~10 mg/L) could promote amaranthin accumulation both in cotyledons and leafs, stems of Amaranthus mangostanus /Lwas the best. But high concentrations of MeJA could inhibit growth of the seedlings and leaf expansion. The following experiments indicated that MeJA could induce amaranthin acculation by promoting the activity of tyrosinase. From above, MeJA could promote amaranthin accumulation both in seedlings of Amaranthus mangostanus L., but application of MeJA had inhibitory effect on plant growth and development.L. Effect of 10 mg L. In this paper, with Amaranthus mangostanus L. as the material, the effect of MeJA (Methyl Jasmonate) on amaranthin synthesis was exploreded. MeJA ( 0.02