Early dietary habits are formative for dietary habits later in life. Maternal personality might be an important factor in unhealthy feeding of children. The current study aims to assess the degree to which the personality trait of negative affectivity in mothers predicts their child's diet at age 18 months. This study is a part of the Norwegian Mother and Child Cohort Study conducted at the Norwegian Institute of Public Health. A total of 27 763 mothers completed 3 repeated assessments of negative affectivity before and after childbirth and of the child's diet when the child was 18 months old. Exploratory factor analysis was used to identify the dietary patterns, and structural equation modeling was used to investigate the relationship with negative affectivity adjusted for socio-demographical variables. Exploratory factor analysis of a foods frequency questionnaire revealed two dietary patterns in the child, labeled unhealthy diet and wholesome diet. The unhealthy diet comprised foods rich in sugar and fat; the wholesome diet comprised foods rich in fibre, vitamins and minerals. Mothers high in negative affectivity were more inclined to feed their child an unhealthy diet. The results were adjusted for maternal age, years of education, relative income, marital status, number of children, having the child in daycare, maternal smoking, maternal body mass index, and child gender. This study shows that a maternal personality trait, negative affectivity, is related to feeding the child an unhealthy diet after controlling for key socio-demographic variables.