A congenital melanocytic nevus (CMN) is a type of melanocytic nevus found in approximately 1% of newborn infants at birth. To remove CMN with a traditional laser without complications is very difficult because of the extension of nevus cells into the deep dermis in this lesion. Unfortunately, there is no standard laser therapy for CMN yet. Therefore, this study was performed to evaluate the efficacy and safety of Dr. Hoon Hur’s Optimal Melanocytic Suicide-4(OMS-4) Parameter Therapy using a 308nm eximer laser for treating CMN. Fifteen Korean patients with CMN were treated with a 308nm eximer laser at a 2-week interval for 30 treatment sessions. The parameters were a spot size of 20mm x 20mm, a fluence of3000mJ/cm2and a pulse rate of 400Hz with 3passes of pulse stacking by 20% overlapping technique over the CMN. At the week of the final treatment, all of the 15 patient with CMN were achieved the complete clearance of dark brown to black pigmented lesions without scarring. There were no recurrences after a follow- up of 12-30 months. We suggest that Dr. Hoon Hur’s OMS-4 Parameter Therapy using a 308nm eximer laseris a safe and effective method without scarring and recurrence in treatment of CMN.