Congenital melanocytic nevus(CMN) constitute a well-known risk factor in the development of malignant melanoma, but melanoma developing in newborn and infants are extremely rare. We describe a case of proliferating nodules within CMN at the age of 13 months. Like our case it is difficult to manage the proliferating lesions within CMN in infants. So we carefully suggest the indications of preventive excision when proliferating lesions occur within CMN as follows; 1) preventive excision is postponed until the age of two when the proliferating lesions are slowly growing, 2) surgical excision is needed when the lesions are rapidly growing exceeding 1 cm in size even though it is before the age of two.