Background: Mangement of melanonychia is often not clear. And there have been no previous study to confirm the efficacy of picosecond laser treatment for melanonychia. Objectives: The aim of this study was to verify the efficacy of 1064 nm picosecond neodymium-doped yttrium aluminum garnet (PSNY) laser in melanonychia without malignant risk. Methods: A retrospective chart review and photo analysis were performed on 9 patients. The patients were included who ruled out malignancy by biopsy or have multiple melanonychia. Also, dermatophyte infection was excluded. Planimetry using Image J software was used to calculate lesion reduction. Clinical improvement was assessed by two blinded dermatologists using a 5-point Global Assessment Scale (GAS). Results: 9 Patients (4 males and 5 females, mean age 38.3 ± 17.0 years, range 20 ~ 65) were analyzed. A total of 38 nails, consisting of 15 finger nails and 23 toe nail, were treated with a 1064 nm PSNY laser, pulse duration of 450 and 750ps, spot size of 3-6 mm, fluence of 1.5-7.0 J/cm2, and pulse rate of 5-10 Hz. The mean interval of treatment was 7.05 ± 5.43 weeks (range: 2 weeks ~ 6 months). The mean treatment session was 3.89 ± 2.15. The average proportion of area of lesions decreased from 33.6% to 26.5% (p < 0.05). The total mean GAS 2.67 ± 0.84 showed fair improvement and no serious adverse event occurred. Conclusion: 1064 nm-PSNY lasers could be an effective option for treatment for benign melanonychia.