Malaria is a tropical disease responsible for the death of hundreds of children daily. Effort geared at eliminating the vector that transmit the causative agent are likely to reduce the incidence of malaria and consequent deaths. This study aims to identify the life cycle stage of Anopheles gambiae most susceptible to the insecticide, lambdacyhalothrin. Different life stages of A. gambiae were exposed to six different concentrations of the insecticide in an Insectary at the National Arbor-virus and Vectors Research Centre, Enugu, Southeastern Nigeria. A total of 650 each, of the different life stages and 350 adults selected from the insectary-bred strains were used for the study. The eggs mortality was monitored at 24 hours interval for 7days. Larvae, pupae and adult mortalities were measured after 6, 12 and 24 hours. Total survival and mortality rates were 6.17 and 0.83, respectively. Average developmental duration was 11.4 and 11.2 days for the parent and F1 generations, respectively. Lambdacyhalothrin concentration higher than 0.001mg/l was highly toxic to the different life stages of A. gambiae compared to the control. The first instar larvae (L₁) stage was the most susceptible to the insecticide and should be considered the most effective target when planning malaria control interventions.