Background:Hyoscyamus nigerL. (Solanaceae) generally known as henbane, is commonly distributed in Europe and Asia. In Turkey, henbane seeds have been used in folk medicine to remove worms from the eyes. The present study aimed to investigate the insecticidal activity ofH. nigerseeds. Methods:n-hexane, ethyl acetate, methanol and alkaloid extracts were prepared from the seeds of the plant and their insecticidal activities onLucilia sericatalarvae were evaluated. EC(50)and EC(90)values of the alkaloid extract were calculated and morphological abnormalities were investigated. Results: Alkaloid extract prepared from the seeds of this plant displayed significant insecticidal activity. EC(50)values ofH. nigerseeds alkaloid extract were found to be 8.04, 8.49, 7.96 mu g/mL against first, second and third instar, respectively. It was determined that malformations of larvae included damaged larvae with small size, contraction and weak cuticle. Furthermore, HPLC analysis was performed on alkaloid extract ofH. nigerseeds and main components of the extract were determined. It was determined that alkaloid extract mainly contain hyoscyamine and scopolamine. Conclusions: These results confirm the folkloric usage of the plant and suggest that the alkaloid content of the plant could be responsible for the insecticidal activity.