According to the World Health Organization’s World Report, approx. 950,000 children and young people < 18 years old die from an injury each year, and unintentional injury deaths account for a large portion of these cases. Here we used medico-legal documents to epidemiologically analyze the cases of unintentional injury deaths among children < 5 years old in Okayama Prefecture, Japan from 2001 to 2015. Age, sex, manner/cause of death, and various circumstances of the incident were investigated. There were 73 unintentional injury deaths during the study period. Drowning (n=29), suffocation (n=24), and transport accidents (n=13) were the major categories of unintentional injury deaths. Twenty-two cases (30.1%) were autopsied. Differences in the characteristics of the unintentional injury deaths by age were observed. Information which cannot be obtained from Vital Statistics was available from medico-legal documents, and detailed characteristics of unintentional injury deaths among children < 5 years old were elucidated. Investigating medico-legal information is one of the meaningful measures for the prevention of unintentional injury deaths among children in Japan.