Background: Indonesia is a country located in the tropics, so Indonesia is an endemic area for mosquito-mediated diseases, such as dengue fever. One of the plants that contain natural ingredients that become mosquito repellent is the fragrant lemongrass plant. Citronella (Cymbopogon nardus) produces an essential oil known as Citronella Oil which contains two important chemical compounds namely citronellal and geraniol, which function as mosquito repellents. The development of topical dosage technology in the formulation of pharmaceutical preparations has led to dosage forms that can be applied in a practical and easy way such as spray gel or spray gel preparations. Methods: Citronella essential oil was prepared in a spray gel preparation and tested for its physical properties. The combination of carbopol 940 and HPMC was optimized using the simplex lattice design method contained in the design expert software version 11 so that 7 run formulas were obtained. Results: The optimum formula of carbopol 940 was 1.25% and HPMC was 0.75% with the optimum response of pH 5.45, viscosity 2.550 cP, and pump delivery 1.64 grams with a desirability value of 1 and the stability test did not find any change. physical preparation either before or after the test. Conclusion: All tests of physical properties of the preparation such as pH, viscosity and pump delivery met the requirements of a good preparation and showed significant values. In the sense that there is no significant difference between the response predicted by the software and the response generated in the experiment. Verification is carried out to ensure that optimization with the software is acceptable.