Studies in urban informal settlements show widespread inappropriate infant and young child feeding (IYCF) practices and high rates of food insecurity. This study assessed the association between household food security and IYCF practices in two urban informal settlements in Nairobi, Kenya. The study adopted a longitudinal design that involved a census sample of 1110 children less than 12 months of age and their mothers aged between 12 and 49 years. A questionnaire was used to collect information on: IYCF practices and household food security. Logistic regression was used to determine the association between food insecurity and IYFC practices. The findings showed high household food insecurity; only 19.5% of the households were food secure based on Household Insecurity Access Score. Infant feeding practices were inappropriate: 76% attained minimum meal frequency; 41% of the children attained a minimum dietary diversity; and 27% attained minimum acceptable diet. With the exception of the minimum meal frequency, infants living in food secure households were significantly more likely to achieve appropriate infant feeding practices than those in food insecure households: minimum meal frequency (adjusted odds ratio (AOR)=1.26,P=0.530); minimum dietary diversity (AOR=1.84,P=0.046) and minimum acceptable diet (AOR=2.35,P=0.008). The study adds to the existing body of knowledge by demonstrating an association between household food security and infant feeding practices in low-income settings. The findings imply that interventions aimed at improving infant feeding practices and ultimately nutritional status need to also focus on improving household food security.