Although many unwed mothers have issues concerning mental health and intellectual ability, little research has focused on their mental and cognitive status. Due to the public stigma attached to unwed mothers in South Korea, they tend to conceal their status and are less likely to seek psychiatric and psychological help. In this context, this study aims to assess the current status of their mental health and intellectual characteristics. A total of 48 unwed mothers from two shelter homes in South Korea agreed to participate in the study. We compared the mental health status of these unwed mothers with that of the general female population. Unwed mothers were more likely than those of the general female population to have mood disorders, post traumatic stress disorder (PTSD), alcohol and nicotine use disorders, and attention-deficit hyperactivity disorder (ADHD). Among the 48 unwed mothers, 20 (41.7%) had an IQ of less than 70, and the mean IQ (78.31) was significantly lower than the normalized mean IQ of the general female population. This study confirmed that unwed mothers dwelling in Korean shelter homes are more likely than the general female population to have mental disorders.