With the current trend of transforming a centralized power system into a decentralized one for efficiency, reliability, and environmental reasons, the concept of a microgrid that integrates a variety of distributed energy resources into distribution networks is gaining popularity. In this paper, we investigate the energy management of a microgrid with renewable energy sources (RESs), such as wind turbines and solar panels, and co-generation in both grid-connected and islanded modes. To address the uncertainties associated with RES power output and grid-connection condition in the microgrid, we propose a two-stage adaptive robust optimization approach to provide a robust unit commitment schedule for co-generation units, with the objective of minimizing the total operating cost under the worst-case scenario of renewable power output and grid-connection condition. The proposed approach ensures robust microgrid operation in consideration of worst-case scenarios, and the over-conservatism can also be mitigated by introducing “budget of uncertainty” parameters. Finally, a case study is conducted to show the effectiveness of the proposed approach.