Mirror therapy has been used to treat phantom limb pain and to improve motor function after stroke. We evaluated the efficacy of mirror therapy in patients with leprosy with paresis. Twenty-four patients with leprosy who presented with unilateral grade 2 disabilities were recruited from July 2016 to November 2016 and randomly assigned. Group A, the mirror group, participated in the mirror therapy, and group B, the control group, were treated with a sham therapy. After the interventions, the paretic muscle/limb function, hand coordination abilities, walking, and abilities to perform activities of daily living were reevaluated with the voluntary muscle testing (VMT) at weeks 3, 6, and 12. In group A, there was an increase in the VMT score from baseline with a median of 2 (interquartile range 0-6) to 3 (2-5) at 3 weeks after initiation of VMT with a further increase to 5 (4-7) at 6 weeks and to 5 (4-8) at 12 weeks, which remained elevated at a median of 6 (5-8) even after 4 weeks after intervention. By contrast, the control group showed the following trend in response to the sham therapy: 2 (1-3) at baseline, 2 (2-4) at 3 weeks after intervention, 3 (3-6) at 6 weeks, 4.25 (3-5) at 12 weeks, and 4 (4-7) at 16 weeks. In group A, VMT scores increased from baseline by 26.9% (p < 0.001), 18.02% (p < 0.001), and 15.46% (p < 0.001) at 3, 6, and 12 weeks, respectively, compared with group B in which VMT scores increased from baseline by 17.13% (p < 0.001), 11.02% (p < 0.001), and 3.93% (p > 0.05) at 3, 6, and 12 weeks, respectively. The muscle strength in mirror group participants improved markedly compared with the control group (post hoc Bonferroni p = 0.027). Mirror therapy is a safe and cost-effective approach in the treatment of paretic limbs of patients with leprosy. This study provides Class IV evidence that mirror therapy improves muscle strength in patients with leprosy associated with paresis.