Cellulase genes are very important for plant-parasitic nematodes to move and feed within their host plants. The pine wood nematode, Bursaphelenchus xylophilus, causes destructive damage by killing pine trees. In this study, by employing dsRNA interference technology, knockdown of a cellulase gene (Bx-eng-1) of B. xylophilus was achieved and the biological effects of RNAi on the nematode were observed. The result showed that, after 24 h soaking, dsRNA of the Bx-eng-1 gene was effectively delivered into the nematode causing a post-transcriptional gene silencing and decrease in cellulase activity. Moreover, the number of F1 generation offspring was reduced significantly when the dsRNA-treated nematodes were cultured on fungal mats. We consider that cellulase is important to B. xylophilus because it not only hydrolyses cellulose of plant cell wall for its parasitism and penetration in host plants, but also influences its feeding, development and propagation on fungal mats.