Abstract The estimation of postmortem interval (PMI) based on the growth patterns of necrophagous arthropods is the main mission of forensic entomology in practice. The larval development rates can be affected by various drugs or toxins, causing deviation in PMI estimate. Ketamine is a widely used anesthetic and recreational drug in Asia, which is rarely focused on in the previous entomotoxicological studies. The present work investigated the effect of ketamine on the development of Lucilia sericata (Meigen) (Diptera: Calliphoridae) by the measurement of body length and weight and the analysis of relationship between the ketamine effect and drug dosage or time interval, meanwhile the difference between ketamine effect on larval body length and weight was also analyzed. Additionally, the preliminary pathological observation of larvae was also employed for evaluating the drug effect in morphology. Significant differences were observed between control and treatment colonies of L. sericata at each life stage, and the effect of ketamine displayed a dosage-and-time-dependent manner, but no differences were noticed between the effects of ketamine on larval body length and weight, which provided a useful indication for larvae sample collection in practice. The pathological observation revealed that ketamine could promote the growth of trophocytes in fat body of L. sericata.