Continuous exposure to sun causes the skin to changes its structure and composition. Sunscreen is a substance that contains protective materials for the skin against sunlight. One of the plants that has the potential as sunscreen is kenitu leaf (Chrysophyllum cainito). This research aims to learn the effectiveness of the sunscreen extraced from kenitu leaf, the physical properties of lotion kenitu leaf extract and the optimum formula of sunscreen lotion kenitu leaf extract. Optimization of the formulation of lotion leaf extract kenitu using software Design Expert version 11 with Simplex Lattice Design method. The independent variables used are stearic acid and Triethanolamine. The responses used in this research were viscosity, pH and SPF. The results showed that kenitu leaf extract has sunscreen activity with a value of SPF 13,126. Software Design Expert produces optimum formula with variations in stearic acid concentration of 3.01% and TEA 2.99% with predicted viscosity of 4939,56, pH of 6,73 and SPF of 13,5333. The optimum formula of kenitu leaf extract lotion produces good physical properties. The optimum formula of kenitu leaf extract lotion has a viscosity 4920 cp, pH 6.85 and SPF 13.4270.