Exclusive breastfeeding (EBF) has been demonstrated to have numerous benefits both to the mother and the infant. Inappropriate feeding practices can have profound consequences for the growth, development and survival of infants and children. EBF protects infants against infections such as respiratory infections, diarrhoea and reduces the risk of the mother developing obesity, breast and ovarian cancer among others. Despite various efforts to promote exclusive breastfeeding, the rate in Kenya is still low at 61% though there has been major improvement. Various research findings have documented inadequate knowledge on exclusive breastfeeding as a contributing factor to the rate of exclusive breastfeeding. However, there is limited scientific data on the gap between the sources of information, content and maternal knowledge on exclusive breastfeeding in relation to exclusive breastfeeding of infants in Kenya’s urban slums. This study aimed to investigate the sources and content of maternal knowledge on exclusive breastfeeding among mothers with infants aged 0-6 months in Kibera urban informal settlements, Nairobi. The study adopted a cross-sectional analytical design and targeted 293 mothers-infant pairs who were selected using systematic random sampling. Simple random sampling was used to select ten health facilities where mothers from Kibera seek health services. A researcher-administered questionnaire was used to collect data on EBF. A key informant guide was administered to the nutritionists to elicit in-depth information on maternal knowledge on exclusive breastfeeding and information gap in relation to practice of exclusive breastfeeding. Focus group discussions (FGDs) were conducted with mothers in various health facilities to build up on the discussion. Data was entered using CS Pro software and analyzed using SPSS version 16 software.