Gliclazide is an antidiabetic drug that has a low solubility in water, so it has low bioavailability. To improve the gliclazide solubility in water, oil in water (o/w) microemulsion system is used. In this study, solubilization of gliclazide in microemulsion that emulsified using saponin-based surfactants from leaf extract of Orthosiphonaristatus (Blume) Miq has been investigated. The oil phase used is palm oil. The preparation of microemulsion was conducted by titration method with various ratios of surfactant and co-surfactant, and ratios of oil with surfactant and co-surfactant mixture. The stability of microemulsion was observed using turbidimeter, microscope, and particle size analyzer (PSA). Solubilization of gliclazide was observed by UV-Vis spectrophotometer and FTIR spectroscopy. The optimum condition of microemulsion formation was resulted in the ratio of surfactant to co-surfactant (Sm) at 8:2, and ratio of surfactant and co-surfactant mixture (Sm) to oil at 10:1. Size distribution of microemulsion particle was confirmed as 10.92 nm, and microemulsion size after gliclazide addition as 91.21 nm using PSA. The optimum result of gliclazide solubility in o/w microemulsion was obtained at 1.6 mg/mL.