Abstract: Alternaria sp. is the main pathogenic fungi of decay in postharvest grape. Different concentrations of natamycin antibacterial liquid on inhibition of the mycelial growth, conidial germination and protection effect of fruit were tested, through growth rate method, hanging drop slide method and in-vivo inoculation method, respectively. The results indicated that suitable concentration of natamycin had the significant inhibition effect on Alternaria solani in postharvest grape ( p < 0.05) .The EC 50 value of antibiotic of mycelial growth and conidial germination was respectively 83.48mg /L and 89.47mg /L. When the inhibitory concentration was 200mg /L, the inhibition ratio of mycelial growth and conidial germination were all above 80%. The in- vivo inoculation experiment indicated that inhibitory concentration of 200mg /L could significantly inhibit rotten caused by Alternaria solani in postharvest grape.In conclusion, natamycin treatment had good inhibitory activity on Alternaria solani in postharvest grape, it could as the potential resource of green preservative in postharvest grape.