Introduction: Dental caries in children is a major problem of mouth disease throughout the world, so too is there currently an increase in health problems in children due to obesity. Human Beta defensing(HBD) has been found in saliva and from several studies stated that HBD aside from being a broad-spectrum antimicrobial can act as an immunomodulator. The purpose of this study is to reveal whether there is a relationship between obesity and HBD-3 salivary concentration in caries patients and caries-free patients. Methods: This cross-sectional observational study was involved 62 children with caries and caries-free, aged 9-11 years, students at Qommarudin Islamic Boarding School, Gresik, East Java Indonesia. dental caries examination, carried out in accordance with World Health Organization (WHO) diagnostic criteria. Body mass index (BMI) was measured from the height and weight of individuals, HBD3 concentrations were tested with an ELISA kit from Bioassay Technology Laboratory (China) from saliva samples. Evaluate the results with the Kruskal Wallis test, followed by the Mann-Whitney test. The level of significance used in this statistical test was 0.05. Results: there was a relationship between BMI level and HBD-3 concentration in the caries group (p <0.05, p = 0.009) with a moderate level of association. but there was no significant relationship in the caries-free group (p> 0.05, p = 0.189). Conclusion: There was an association between BMI and HBD-3 salivary concentration in caries patients but there was no relationship in the caries-free group.