An entomopathogenic fungus, Paecilomyces javanicus was isolated from diseased brown planthopper (Nilaparvata lugens Stal.) in Northern Vietnam. Its colony growth was moderately fast on PDA medium, attaining up to 5.2 cm diameter of after 12 days at 30oC. Its shape was found that as a powder to floccose, white-cream at first then becoming pale violet with age. Conidiophores erect, arising from the aerial mycelium, bearing phial ides in whorls with 2 to 3 of branches. Phialides consists of a cylindrical basal part, tapering into a thin neck. Conidia cylindrical to fusiform, smooth-walled, hyaline. The capacity of parasitism on BPH by Paecilomyces javanicus was accounted as 84.4 percent in the laboratory conditions. The mortality rate of WBPH and BPH infected by fungus Paecilomycesjavanicus reached to 79.1 percent and 74.9 percent, respectively in greenhouse conditions.