Our previous study found that microRNA-21a-5p (miR-21a-5p) knockdown could improve the recovery of motor function after spinal cord injury in a mouse model, but the precise molecular mechanism remains poorly understood. In this study, a modified Allen's weight drop was used to establish a mouse model of spinal cord injury. A proteomics approach was used to understand the role of differential protein expression with miR-21a-5p knockdown, using a mouse model of spinal cord injury without gene knockout as a negative control group. We found that after introducing miR-21a-5p knockdown, proteins that played an essential role in the regulation of inflammatory processes, cell protection against oxidative stress, cell redox homeostasis, and cell maintenance were upregulated compared with the negative control group. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis identified enriched pathways in both groups, such as the oxidative phosphorylation pathway, which is relevant to Parkinson's disease, Huntington's disease, Alzheimer's disease, and cardiac muscle contraction. We also found that miR-21a-5p could be a potential biomarker for amyotrophic lateral sclerosis, as miR-21a-5p becomes deregulated in this pathway. These results indicate successful detection of some important proteins that play potential roles in spinal cord injury. Elucidating the relationship between these proteins and the recovery of spinal cord injury will provide a reference for future research of spinal cord injury biomarkers. All experimental procedures and protocols were approved by the Experimental Animal Ethics Committee of Shandong University of China on March 5, 2014.