In order to evaluate the effect of ribozymes on suppressing BmNPV, triplet ribozyme (R426) targeting the BmNPV immediate early gene (IE) was designed. In vitro cleavage experiment showed that R426 transcript was able to cleave the target sequence specifically. Expression experiment indicated that R426 extracted from Bm-N cell can also cleave the target specifically and cause about 30% reduction of BmNPV polyhedra in transfected cell.