Spinal cord injury (SCI), which is characterized by excessive inflammatory cell infiltration and accumulation of oxidative substance, would severely impede neurological functional recovery and lead to permanent and profound neurologic deficits and even disability. Methylprednisolone (MP) is the most commonly used clinical anti-inflammatory drug for SCI treatment, but high doses are typically required that can cause severe side effects. Here, we developed a carrier-free thioketal linked MP dimer@rutin nanoparticles (MP-TK@RU NPs) which can achieve combined SCI treatment by coassembling reactive oxygen species (ROS) cleavable MP dimers and rutin. This proposed nanodrug possesses the following favorable advantages: (1) the carrier-free system is easily accessible and has a high drug-loading capacity, which is preferred by the pharmaceutical industry; (2) The ROS-cleavable linker increases the efficiency of targeted drug delivery to the injury site; (3) Rutin, a type of plant-derived natural flavonoid with good biocompatibility, anti-inflammatory, and antioxidant properties, is codelivered to enhance the therapy outcomes. The obtained MP-TK@RU NPs exhibited potent anti-inflammatory and antioxidative properties both in vitro and in vivo, demonstrating superior locomotor function recovery and neuroprotective efficacy in rats with SCI. This carrier-free nanodrug is anticipated to provide a promising therapeutic strategy for clinical SCI treatment.