The efficacy of low-level laser therapy (LLLT) was evaluated in a total of 66 patients with mild to moderate carpal tunnel syndrome (CTS) with a double-blinded randomized controlled study. The patients were randomly assigned into two groups. Group I received 15 sessions of a gallium-aluminum-arsenide laser treatment at a dosage of 18 J per session over the carpal tunnel area with neutral wrist splint. Group II received placebo laser therapy with neutral wrist splint. The patients were evaluated with the following parameters: (1) clinical parameters which consisted of visual analog scale, symptom severity scale, functional status scale, and pinch strength and grip strength before the treatment and at 5- and 12-week follow-ups and (2) electroneurophysiological parameters from nerve conduction study which were evaluated before the treatment and at 12-week follow-up. Fifty nine patients (112 hands: unilateral CTS = 6 hands and bilateral CTS = 106 hands) completed the study. Both groups I and II had n = 56 hands. Improvements were significantly more pronounced in the LLLT-treated group than the placebo group especially for grip strength at 5- and 12-week follow-ups. At 12-week follow-up, distal motor latency of the median nerve was significantly improved in the LLLT group than the placebo group (p < 0.05). LLLT therapy, as an alternative for a conservative treatment, is effective for treating mild to moderate CTS patients. It can improve hand grip strength and electroneurophysiological parameter with a carry-over effect up to 3 months after treatment for grip strength of the affected hands.