In order to investigate the effect of melatonin on enzymatic browning of fresh cut yam, fresh pieces of the cut Chinese yam of were treated by 1, 2, 3 mmol/L melatonin solution respectively and dipped in water as control. They were stored at room temperature(25 ℃) for 4 days and the color parameter(L*, a*, b*, total color difference value ΔE), polyphenol oxidase(PPO) activity, peroxidase(POD) activity, phenylalanine ammoniase(PAL) activity, catalase(CAT) activity, H2O2 content, lipoxygenase(LOX) activity, malondialdehyde(MDA) content, DPPH free radical scavenging rate and ABTS free radical scavenging rate were selected to be measured. The results showed that melatonin treatment could inhibit the activities of PPO, POD, PAL and LOX in fresh cut yam. After 4 days of storage, the PPO, POD, PAL and LOX activities of samples treated with 3 mmol/L melatonin were 51.6%, 65.6%, 27.1% and 24.6% lower than those of the control group, respectively. Melatonin treatment could also reduce the H2O2 and MDA contents in yam. After 4 days of storage, the H2O2 and MDA contents in the sample treated with 3 mmol/L melatonin decreased by 84.8% and 21.0%, respectively, compared to the control group. Melatonin treatment could enhance CAT activity in yam. After 4 days of storage, the CAT activity of the sample treated with 3 mmol/L melatonin was 1.96 times higher than that of the control group. Melatonin treatment could enhance the DPPH and ABTS free radical scavenging ability. After 4 days of storage, the DPPH and ABTS free radical scavenging rates of samples treated with 3 mmol/L melatonin were increased by 20.6% and 18.7%, respectively, compared to the control group. Melatonin treatment could also effectively delay the browning on the surface of fresh cut yam, and its effect was concentration dependent. 3 mmol/L of melatonin had the best color protection effect. When stored for 4 days, the L* value of the sample treated with 3 mmol/L of melatonin was 32.5% higher than that of the control group, a*, b*, ΔE was 74.0%, 50.7%, and 67.3% smaller than the control group, respectively. The relevant analysis results showed that there was a highly significant correlation between ΔE and L*, a*, b*, PPO activity, POD activity, PAL activity, H2O2 content and MDA content, as well as a significant correlation with ABTS free radical scavenging ability.