Background: Sunscreen or sunscreen can be used to minimize the negative impact caused by exposure to UV rays. Kepel leaves (Stelechocarpus burahol (Bl.) Hook.F. & Th.) contain flavonoid compounds, where flavonoids are closely related to photoprotective activity due to the presence of chromophore groups that can absorb UV A and UV B rays. This study aims to determine the activity of sunscreens. Kepel leaf extract lotion preparation. Methods: Making kepel leaf extract using maceration method with 70% ethanol solvent. Optimization of sunscreen formula using the simplex lattice design (SLD) method based on various levels of 2 factors, namely cetyl alcohol and glycerin with response parameters used include SPF, pH and viscosity values. The data obtained were verified with one sample t-test to determine the difference between the predicted results from the optimization method and the test results. Results: Based on the test on Kepel leaf extract at a concentration of 200 ppm, the results showed an SPF value of 15,119 (ultra protection). The optimum formula predicted by the simplex lattice design method obtained a concentration of 2% cetyl alcohol and 8% glycerin. Kepel leaf extract lotion has an SPF value of 13.523 ± 0.002, pH of 6.916 ± 0.02 and viscosity of 2360 ± 34.64 cp. Verification of the optimum formula prediction results from the optimization method has an no significant difference with the test results. Conclusion: Kepel leaf extract can be used as a sunscreen with maximum protection and from the verification results on the optimum formula for lotion preparation, it can be stated that the simplex lattice design method can be used to predict the response parameters of Kepel leaf extract lotion preparations.