The purpose of this experimental study was to evaluate possible upgrading effects of systemic creatine monohydrate administration on the reinnervation of denervated muscle. At the same time, the protective effect of the agent on denervated muscle until ultimate reinnervation after nerve repair was quantified. The functional outcome of muscle reinnervation after creatine monohydrate application was compared with a control group. Forty adult Wistar rats weighing 180 to 220 g were used. The right sciatic nerve was dissected, exposed, and cut at the level of the midthigh in all rats. The experimental design consisted of two groups: experimental (animals were fed creatine monohydrate) and control (gavage feeding was provided by saline). Both groups were divided into two subgroups: subgroups A and B for the experimental group, and subgroups C and D for the control group. In subgroups A and C, the nerves were repaired with four 10-0 epineurial stitches. In subgroups B and D, both the proximal and distal ends of the nerves were ligated and no neural anastomosis was performed. In the experimental groups (subgroups A and B), the rats were fed by daily supplementation of oral creatine monohydrate, 300 mg/kg body weight. In the controls (subgroups C and D), oral supplementation was provided by saline. Functional recovery was evaluated using walking track analysis, pinching test, and limb circumference and toe contracture measurements at the end of 6 months, after which the rats were sacrificed and nerve specimens from both ends of the repair sites and the whole gastrocnemius muscle were obtained to document the results of the histomorphometric and histochemical studies, including light microscopic examinations and muscle weight measurements. The mean functional recovery values in subgroups A, B, C, and D were 91 percent, 80 percent, 87 percent, and 59 percent, respectively. Functional recovery improved significantly in the experimental groups (in both the surgically repaired and unrepaired subgroups), compared with the control groups (p<0.05). The pinching test revealed a statistically significant difference in nerve conduction between the experimental and control groups (p<0.05). The limb circumference ratio of the surgically treated side to the untouched side in subgroups A, B, C, and D were noted as 0.95, 0.89, 0.91, and 0.87, respectively, and the difference between the experimental and the control groups was statistically significant (p<0.05). The differences between subgroups A and B, C and D, A and C, and B and D were also significant. The surgically repaired and creatine-supplemented subgroups demonstrated the best results in toe contracture index. The muscle weight measurement results were concordant with the results of the limb circumference ratio. In both surgically repaired subgroups (subgroups A and C), there were qualitatively significant amounts of myelinated fibers in the nerve distal to the anastomotic site; there were no myelinated fibers in the distal stumps of subgroups B and D. Histochemical analyses of the contents of the muscle fiber types also revealed no significant difference. Overall, the results showed the useful effect of oral creatine supplementation on both surgically repaired and unrepaired nerve injuries. The best results were obtained from surgically repaired nerve injuries and also from the systemic creatine-supplemented subgroups. This study confirms that systemic administration of creatine monohydrate has a protective and upgrading effect on the functional properties of denervated muscle, especially in surgically reinnervated subjects.