Two species of leaf-miner flies belong to family Agromyzidae were Liriomyza sativae Blanchard and Chromatomyia horticola Goureau, and six parasitoids belong to two families Braconidae and Eulophidae were found on cucumber in 2013 in Hoang Hoa, Thanh Hoa. Leaf-miner flies of family Agromyzidae damaged during the growth and development of cucumber, the rate of damage gradually increased to the end of the crop at harvest and the most destructive in the period of flowering - fruiting, cucumbers of the main crop (Spring and Winter) were more damaged than unseasonable cucumbers (Summer and Autumn). Parasitoids appeared as soon as leaf-miner flies incurred, then the rate of parasitoids gradually increased along with the increase in density of leaf-miner larvae, parasitic rate also peaked in the period flowering - fruiting at 47.56 percent (Liriomyza sativae) and 48.37 percent (Chromatomyia horticola).