Background: Severe onychomycosis in the elderly is a common condition and generally difficult to treat. Long-pulsed Nd:YAG(LPNY) laser has been found to be useful in the treatment of onychomycosis. Objectives: We sought to evaluate the effectiveness of 1,064nm LPNY laser in the treatment of severe onychomycosis. Methods: Fourty nails in 13 patients with severe onychomycosis were divided into two groups. Each group was received eight treatment sessions at one-week intervals with 1,064nm LPNY laser. Parameters for group A were 0.3ms pulse duration, 5mm spot size, 16J/cm2 fluence and 10Hz frequency, and those for group B were 0.6ms, 2mm, 225J/cm2 and 5Hz. Clinical and mycological clearance were evaluated at 12 and 24 weeks after initial treatment. Results: Clinical improvements at 12 and 24 weeks presented 47.6% and 57.1% in group A, 26.3% and 36.8% in group B. In the treated nails with clinical improvement, mycological positive rates at 24 weeks were approximately 40% in both groups. Conclusion: The treatment of onychomycosis using 1,064nm LPNY laser were incomplete in clinical and mycological improvement, and it could imply a lot of potential recurrence. We suggest that 1,064nm LPNY laser for severe onychomycosis should need additional or combined therapy with other therapeutic options.