Obesity, especially in pregnant women, could cause many health problems regarding both the individual and the baby related to the tendency not to exclusively breastfeed in the future. This study aim to know the association between maternal obesity and exclusive breastfeeding (EBF) practice. This study was an observational analytic (non-experiment) with a historical cohort design, carried out between November 2018-June 2019. The population was all first trimester pregnant women between March 2016-December 2017 who had first antenatal care in Tegalrejo and Mantrijeron Primary Health Care. The sample used was 130 respondents divided into two groups, 68 as exposed and 62 as non-exposed group. Sampling technique used was multistage random sampling. This study analyzed six variables, which were maternal obesity, age, education, occupations, knowledge, and attitude. Data collected using form and questionnaire. Chi-square test and logistic regression were used in data analysis. There was an association between maternal obesity and EBF practice. After controlling the attitude variable, maternal obesity had significance (p=0,002) toward EBF practice. The failure of EBF was higher 1,74 times in obese mother (RR=1,74).