Abstract: In order to improve the biocontrol efficacy of biological control agents (BCA), the authors used Purpureocillium lilacinum YES and Clonostachys rosea 67-1 in combination to control cucumber root-knot nematode caused by Meloidogyne incognita. Dual culture tests on plates of PDA and cucumber root extraction media demonstrated that the two fungi were non-antagonistic to each other. Determination of parasitized eggs in sterile 24-well cell culture plates showed that 51.0% of eggs were parasitized by YES, higher than that parasitized (44.0%) by 67-1, after inoculation with 2×10⁶ spores per milliliter. Tests on mortality showed that 100% of J2 died after treatment with fermentation filtrates of 67-1 for 48 h, higher than that (77.4%) by filtrate of YES. The control efficacies of the two fungi alone or in combination were tested in greenhouse and field by mixing their powders with growth-medium of vegetable seedlings and hole-applying of 50 g powders at final concentration of 10⁶ conidia/g during transplantation. Investigation of galls on the cucumber roots indicated that the control efficacy was related to the initial population of nematode eggs or juveniles inoculated in soil. At high inoculation density of J2 at 1000 J2/100 g soil, all BCA treatments could not perform good control, with efficacy only 20%—30%. According to blissing independence model, antagonistic effect was got between YES and 67-1 under this condition. While at the nematode density of 398 eggs/100 g of soil in field trail, YES and 67-1 powders in combination could significantly suppress gall numbers on cucumber root system and the control efficacy reached 63.7%, higher than single use. According to blissing independence model, additive effect was obtained for the combined use. These results suggested that combined usage of the two biocontrol agents could lead to a delay ofinfection by nematodes, but this was affected by the developmental stage and density of the nematode in soil. The results are of significance in developing complex BCA preparations and their delivery system in field.