Abstract: Agricultural Antibiotic 120 (AA120) 4 % aqueous solution , developed by Institute of Biological Cont rol of CAAS , has positive effect on four leaf diseases of apple and pear trees Physalospora pi ricola , Glomerella ci ngulata , Alternaria mali and Venturia pyrina in lab and fields. The methods of efficacy t rial in lab were dilution method and spore germination method. According to China′s National Standard GB/ T17980-2000 , the efficacy t rial was done in Henan and Shanxi province. The EC50 of this new product to the four diseases were respectively 1. 92 , 5. 56 , 17.14 and 4. 36mg/ L in lab. The effect of 68mg/ L AA120 on the four diseases were respectively 75.33 % , 90.16 % , 73.22 % , 81.61 % in fields. The effect of 50mg/ L AA120 on them were respectively 66.67 % ,86.53 % , 66.52 % and 79.31 % in fields. The effect of 40mg/ L AA120 on them were respectively 59.67 % , 76.68 % , 60.78 % and 71.26 % in fields. The effect of 560mg/ L Duojunling (pesticide) on them were respectively 66.00 % , 89.64 % , 36.73 % and 69.89 % in fields. Then through comprehensive consideration of cost and the fields efficacy , we estimate that the best concent ration of AA120 to cont rol G. ci ngulata and V . pyrina is 50mg/ L , to P. pi ricola and A . mali is 68mg/ L.