Norwalk virus and Noro virus are members of the Caliciviridae. These viruses are morphological similarity in each other and shows small round structure. These viruses also are well known as main pathogens of acute infectious gastroenteritis. Clinical features include an incubation period of 24 of 48 hours and illness period of 18 to 72 hours with vomiting and diarrhea in most patients and high secondary attack rates. Oral transmitted infection occurs contaminated water and foods. In our country, outbreak of Noro virus-related gastroenteritis are reported sometimes in hospital and nursing home from winter to early spring seasons. This article are described to the morphlogy, physical characteristics, epidemiology, and clinical manifestation relating to Norwalk virus and Noro virus.