Exclusive breastfeeding (EBF) is very crucial for the health of infant as well as mother. However, the prevalence ofexclusive breastfeeding is very low especially among working mother. Since the prevalence of EBF might be influenced bythe level of knowledge on EBF, researcher comes to critical thinking to conduct this study to evaluate level of knowledgeon EBF among working mother. A cross sectional design study was carried out to determine knowledge level on exclusivebreastfeeding among working mother, and its relationship with demographic data in Hospital Canselor Tuanku Muhriz(HCTM). A total 283 respondents were recruited to participate in this study. The respondents’ knowledge level on exclusivebreastfeeding was identified using Kim & Chapman (2013) Questionnaire on Knowledge and Practice about ExclusiveBreastfeeding. The result showed that majority of the respondents (56.9%) had high knowledge on exclusive breastfeeding.For demographic data, factors such as age, level of education, and family income had shown a significant association (p< 0.05) with level of knowledge on exclusive breastfeeding. In conclusion, the level of knowledge of EBF was identifiedamong working mother, yet it has been influenced by mother’s sociodemographic background.