Objective: To evaluate bone antiresorptive effect of oleanoic acid (OA) in the rankl:HSE:CFPtransgenic medaka (Oryzias latipes) fish model for osteoporosis. Method: Transgenic larvaewere treated with OA at different concentrations from 7 days post fertiliztion (dpf) onwards,heatshocked at 9 dpf to induce osteoporosis-like phenotype and fixed at 11 dpf to stained formineralized bone matrix. Length of the first 15 neural arches were measured and indexes of bonemineralization (IM) and indexes of mineralization protection (IP) were calculated to evaluate boneprotective effect of OA. Results: Mean IM of larvae treated with OA at concentration of 7.5 μM,12.5 μM, 15 μM or 20 μM was significantly higher than that of the DMSO control larvae and similarto that of alendronate-treated larvae. Moreover, 15 μM or 20 μM OA has higher IP than 25 μg/mlalendronate, a common anti-osteoporosis drug. Conclusion: Oleanoic acid has bone protectiveeffect in the Rankl-induced osteoporosis medaka and this bone protective effect is comparable toalendronate.