Heat shock protein 90 (Hsp90) plays a very important role in facilitating the replication of many viruses. Until now, little has been known about the role of Hsp90 in Bombyx mori virus infection. In this study, we explored the role of BmHsp90 in B. mori nucleopolyhedrovirus (BmNPV) replication. We found that BmHsp90 inhibition by geldanamycin (GA) significantly reduced the BmNPV titre, the protein expression level of BmNPV nucleocapsid protein 39 (VP39) and the transcript level of BmNPV genes. Silencing the hsp90 gene in BmN cells by small interfering RNA suppressed BmNPV replication whereas overexpression of hsp90 promoted the replication of BmNPV. After inhibition of Hsp90, the expression of three key genes signal transducing activator of transcription (stat), suppressor of cytokine signalling protein 2 (socs2), socs6 involved in the Janus kinase/STAT pathway significantly changed, with up‐regulation of stat and down‐regulation of socs2 and socs6. In addition, the expression of two antiapoptosis genes, BmNPV inhibitor of apoptosis protein1 (BmNPV‐iap1) and Bmiap2, was greatly decreased in GA‐treated cells, whereas their expression was significantly increased in hsp90‐overexpressed silkworm larvae. Our results indicated that inhibition of Hsp90 can suppress BmNPV proliferation in B. mori. Our findings may provide new clues to elucidate the molecular mechanisms of silkworm–virus interactions. Inhibition of Bombyx mori heat shock protein 90 (BmHsp90) by geldanamycin and RNA interference can suppress B. mori nucleopolyhedrovirus (BmNPV) proliferation. Overexpression of BmHsp90 can promote BmNPV proliferation in B. mori. Inhibition of BmHsp90 can change the transcript level of genes related to the Janus kinase/signal transducing activator of transcription/ immune pathway and cell apoptosis.