Introduction This study aimed to examine whether administration of coenzyme Q10, an antioxidant, improves insulin resistance in patients with prediabetes. The study design was a pilot single-center, randomized, double-blind, placebo-controlled trial. Methods This pilot single-center, randomized, double-blind, placebo-controlled trial included a total of 80 adults (aged ≥20 years) with impaired glucose tolerance. After the initial screening visit, subjects were assigned to either the experimental (n = 40) or placebo (n = 40) group via simple randomization. Insulin resistance was represented as the insulin resistance index estimated by homeostasis model assessment (HOMA-IR). Results After the 8-week treatment period, the coenzyme group exhibited a significant decrease in the HOMA-IR (P < .001). The free oxygen radical and coenzyme Q10 concentrations were found to correlate significantly (P < .001). However, no significant changes in fasting blood glucose, insulin, and glycated hemoglobin levels were observed in either group. Additionally, no adverse events occurred in either group. Conclusion Patients with prediabetes who were administered coenzyme Q10 showed a significant reduction in HOMA-IR values. Therefore, administration of coenzyme Q10 in patients with impaired glucose tolerance may slow the progression from prediabetes to overt diabetes.