Aims:  To evaluate the biocontrol efficacy of culture filtrate containing chitinase from Trichoderma harzianum against Heliothis. Methods and Results:  T. harzianum was cultured by submerged fermentation using colloidal chitin as sole carbon source. The ability of the culture filtrate to hydrolyse colloidal chitin indicated the presence of chitinase as one of its components. Biocontrol assay on Heliothis showed that the culture filtrate is a potent antifeedant as it reduced the feeding rate and body weight of the larvae. It reduced the successful pupation and increased larval and pupal mortality in a dosage‐dependent manner when applied topically. The highest mortalities (70%) were recorded for groups treated with 2000 U ml−1 chitinase activity. The percentage of adult emergence was zero for the highest chitinase concentration (2000 U ml−1) tried. Conclusions:  The studies showed that the culture filtrate containing chitinase from T. harzianum is capable of negatively affecting the growth and metamorphosis of Heliothis larvae. Significance and Impact of the Study:  In view of the need for safer and environmentally friendly pest management tools, the present study could help in the development of enzyme‐based biopesticides against Heliothis.