The root mealybug is a serious insect pest on black pepper. Black pepper root mealybug lives in the soil and often create “crust over” when causing severe damage, therefore, it is difficult to detect and control by chemical method. Purple fungi Paecilomyces sp. is the entomophathogenic fungi and often lives in soil. This study aimed to isolate, select and evaluate the effectiveness of purple fungus Paecilomyces sp. on black pepper root mealybugs in Dak Lak province. The study isolated and identified 4 strains of Paecilomyces sp. capable of parasitizing and causing root mealybugs of black pepper in Dak Lak province, including PB1, PB2, PB3 and PL4. In which, PB1 strain has highly pathogenic to both nymph and adult of root mealybug stage. In the laboratory, the conidial concentration of PB1 strain greatly influenced the mortality of larvae and adults of black pepper root mealybugs. The PB1 concentration at the dose of 1x109 conidia/ml caused the highest mortality of black pepper root mealybugs.