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The oxidative potential (OP) of ambient particulate matter (PM) is a common metric for estimating PM toxicity and linking PM exposure to adverse health effects. Organic aerosol (OA), a dominant fraction of ambient PM worldwide, may significantly contribute to PM toxicity. Here, we investigated the source‐based OA components contributing to the OP of PM in the urban (Beijing, summer and winter) and rural (Gucheng, winter) environments of the North China Plain (NCP). Various OA components as identified by the aerosol mass spectrometer/aerosol chemical speciation monitor (AMS/ACSM), transition metals, and black carbon were compared with the OP of PM measured by dithiothreitol assays. The results consistently demonstrate the importance of OA as a contributor to PM's OP in both urban and rural NCP environments. Higher intrinsic OP was observed in winter Beijing than in summer, possibly due to OA being predominantly from anthropogenic sources in winter. Furthermore, different OA components were found to drive the response of OP in the two environments. More‐oxidized oxygenated OA (MO‐OOA), cooking OA, and oxidized primary OA (during winter) are the OA contributors to OP in the urban environment, with a dominant contribution from MO‐OOA. In contrast, biomass burning OA (BBOA) and OOA play a major role in the OP in the rural environment, with BBOA making the largest contribution. Overall, this work highlights the significance of OA in determining PM's OP and calls for more work to reveal the sources and characteristics of OA components contributing to OP across different regions. Plain Language Summary: Ambient fine particulate matter (PM2.5) is a top risk factor for human health. The oxidative potential (OP) of PM2.5 is widely used to estimate PM2.5 toxicity and link PM2.5 exposure with its adverse health effects. Organic aerosol (OA) constitutes a major fraction of PM2.5 and can contribute substantially to the OP of PM2.5. But OA is also a complex mixture comprised of thousands of compounds each with widely different health effects. Here, we reveal the key OA components driving the OP in the urban and rural environments of the NCP. We find that more‐oxidized oxygenated OA, which is highly oxidized and can be formed from multiple atmospheric processes, is a dominant contributor to the OP in the urban environment. In contrast, biomass burning OA makes the largest contribution to the OP in the rural environment. In sum, different OA components are found to be the main drivers of the OP in the two environments. More studies are warranted to further our understanding of the causes, sources, and characteristics of the PM2.5 OP over a wide range of geographical regions. Key Points: Seasonal and spatial variations of oxidative potential (OP) of ambient particulate matter are foundOrganic aerosol (OA) is an important contributor to the oxidative potential in both urban and rural environmentsMore‐oxidized oxygenated OA and biomass burning OA have a dominant contribution to the OP in urban and rural environments, respectively [ABSTRACT FROM AUTHOR]