There exists an emergency clinical demand to overcome TRAIL/Apo2L (tumor necrosis factor-related apoptosis-inducing ligand) resistance, which is a major obstacle attributed to insufficient level or mutation of TRAIL receptors. Here, we developed an iron oxide cluster-based nanoplatform for both sensitization and MR image-guided evaluation to improve TRAIL/Apo2L efficacy in colorectal cancer, which has an inadequate response to TRAIL/Apo2L or chemotherapy. Specifically, NanoTRAIL (TRAIL/Apo2L-iron oxide nanoparticles) generated ROS (reactive oxygen species)-triggered JNK (c-Jun N-terminal kinase) activation and induced subsequent autophagy-assisted DR5 upregulation, resulting in a significant enhanced antitumor efficacy of TRAIL/Apo2L, which confirmed in both TRAIL-resistant HT-29, intermediately resistant SW-480 and sensitive HCT-116 cells. Furthermore, in a subcutaneous colorectal cancer mouse model, the in vivo tumor retention of NanoTRAIL can be demonstrated by MR T2 weighted contrast imaging, and NanoTRAIL significantly suppressed tumor growth and prolonged the survival time without observable adverse effects compared with control and TRAIL/Apo2L monotherapy. Importantly, in the study of colorectal cancer patient-derived xenograft models, we found that the NanoTRAIL treatment could significantly improve the survival outcome with consistent ROS-dependent autophagy-assisted DR5 upregulation and tumor apoptosis. Our results describe a transformative design that can be applied clinically to sensitize Apo2L/TRAIL-resistant patients using FDA-approved iron oxide nanoparticles.