AIM: This study aims to develop and assess the therapeutic potential of oleanolic acid nanoparticles (OA NPs) in treating ulcerative colitis (UC). MATERIALS & METHODS: OA NPs were synthesized using an emulsion solvent evaporation method, forming spherical nanoparticles with an average diameter of 138.1 nm. The nanoparticles were designed to target the colon through the enhanced permeability and retention (EPR) effect. Network pharmacology and molecular docking identified key inflammatory pathways, and in vitro (RAW264.7 cells) and in vivo (DSS-induced UC mouse model) experiments evaluated their anti-inflammatory effects and therapeutic efficacy. RESULTS: OA NPs successfully targeted the colon and demonstrated improved bioavailability. In vitro experiments showed that OA NPs reduced oxidative stress and inflammation by downregulating pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and promoting macrophage polarization from M1 to M2. In the DSS-induced UC mouse model, oral administration of OA NPs significantly alleviated colitis symptoms, improved colon length, reduced inflammation, and mitigated tissue damage. CONCLUSION: OA NPs mitigate UC pathology through targeted delivery, enhanced stability, and modulation of inflammatory pathways, providing a promising approach for UC treatment. Further studies are needed to evaluate their long-term safety and clinical applicability.