To decrease infant mortality and incidence of malnutrition, the Government of Indonesia fixed target of exclusive breastfeeding for 6 months was 80%. Breast-feeding program in the city of Magelang can not reach 40%. The purpose of this study was to determine the relationship between demographic factors, knowledges of mothers with exclusive breastfeeding. This study was an observational study using cross-sectional approach. The collection of data obtained through interviews with 113 mothers of infants aged 0-6 months using a questionnaire, sampling was done by stratified random sampling method. A lot of 27,4% of respondents gave breastfeeding exclusively. The majority of respondents are very poor in exclusive breastfeeding informations. There is relationship between mother education level (p = 0,043), family income (p = 0,021), and knowledge about exclusive breastfee-ding (p = 0,015) with exclusive breastfeeding