BACKGROUND: Mosquito control is essential in preventing mosquito-borne diseases. Natural substances originated from plants possessed the great potential of insecticidal properties, the resistance occurs at a slower rate compared to the synthetics, with less toxicity to other living creatures. AIM: This study aimed to identify the fraction of ketapang leaf (Terminalia catappa L) with larvicidal activity on Aedes aegypti instar III larvae, the concentration of ketapang active leaf fraction comparable to temephos, and Lethal Concentration 50 (LC50). METHODS: This study was experimental in vitro. The experiment was performed with five different concentrations of ketapang leaf water-ethanol fraction, i.e. 1200 ppm, 1400 ppm, 1600 ppm, 1800 ppm, 2000 ppm. Observation of morphological damage of mosquito larvae was conducted with the microscope and ImageJ application. Data analysis was performed using One Way ANOVA. LC50 was determined with probit analysis. RESULTS: Phytochemical screening revealed a water-ethanol fraction of ketapang leaf contained tannin, saponin, and flavonoid compounds. The water-ethanol fraction with 1800 ppm concentration possessed significant larvicidal effect comparable to temephos. Probit test revealed an LC50 value of 1563.082 μg/ml. CONCLUSION: Water-ethanol fraction of ketapang leaf possessed high biolarvicidal activity against Ae. aegypti larvae instar III comparable to temephos.