Nitro-fatty acids are electrophilic fatty acids produced in vivo from nitrogen peroxide that have many physiological activities. We recently demonstrated that nitro-fatty acids activate the Keap1-Nrf2 system, which protects cells from damage owing to electrophilic or oxidative stresses via transactivating an array of cytoprotective genes, although the molecular mechanism how they activate Nrf2 is unclear. A number of chemical compounds with different structures have been reported to activate the Keap1-Nrf2 system, which can be categorized into at least six classes based on their sensing pathways. In this study, we showed that nitro-oleic acid (OA-NO2), one of major nitro-fatty acids, activates Nrf2 in the same manner that of a cyclopentenone prostaglandin 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) using transgenic zebrafish that expresses green fluorescent protein (GFP) in response to Nrf2 activators. In transgenic embryos, GFP was induced in the whole body by treatment with OA-NO2, 15d-PGJ2 or diethylmaleate (DEM), but not with hydrogen peroxide (H2O2), when exogenous Nrf2 and Keap1 were co-overexpressed. Induction by OA-NO2 or 15d-PGJ2 but not DEM was observed, even when a C151S mutation was introduced in Keap1. Our results support the contention that OA-NO2 and 15d-PGJ2 share an analogous cysteine code as electrophiles and also have similar anti-inflammatory roles.