BACKGROUND: The national coverage of exclusive breastfeeding (EBF) in Indonesia still low and one of the causes was from lactating mothers’ factor. The EBF coverage in Bantul Regency, Yogyakarta was still below the national target (80%). Breast milk has been proven to be the best source of nutrition that provides various benefits for babies, mothers, families, and the country. Benefits for babies are better immunity, as well as intelligence and mental development. AIM: The research aims to analyze the determinants of exclusive breastfeeding in lactating mothers in Yogyakarta, Indonesia. METHODS: An observational analytical research with cross-sectional design in Bantul Regency, Yogyakarta, Indonesia. The population was lactating mothers in Sewon and Srandakan, Bantul uses a sample of 100 people with purposive sampling method. Data were collected with questionnaires and analyzed with Chi-square test and Multiple Logistic Regressions using Statistical Package for the Social Sciences-16. The husband’s support (informational support, award support, instrumental support, and emotional support) is declared not supportive if the total value is less than the mean. RESULTS: Factors that related to EBF were husband’s informational support, husband’s total support, and the promotion of infant formula (p < 0.05). The variable that proven to be the determinant of EBF was the promotion of infant formula (odds ratio = 4.47, 95% CI = 1.50–13.30) in probability equal to 0.007. CONCLUSION: The study showed a low prevalence of EBF. Totally support of the husband, especially the information support was needed by lactating mothers. The most influential factor that proved to be a determinant of EBF in lactating mothers was the promotion of infant formula. It was necessary to prevent and stop all ways of promoting formula milk, especially in healthcare facilities or through advertisements and involving community leaders or well-known figures to campaign for the benefits of EBF for the community through various media.