Background/Aim. Early childhood caries (ECC) is a special form of caries in primary dentition that affect teeth after eruption, with rapid progression, later symptomatology and numerous complications. The aim of this study was to investigate the frequency of ECC among different ethnic groups of preschool children in the South Bačka District. Methods. The survey was performed as a crosssectional analytical study on the sample of preschool children of both sexes and different ethnic groups in the South Bačka District. The diagnosis and the clinical form of ECC was defined by dental check-ups according to the modified Wyne's criteria: the initial form (type 1) shows carious lesions without disturbing the surface structure of the tooth enamel, the moderate form (type 2) shows carious lesions affecting one or two teeth or their surfaces, the middle form (type 3) shows carious lesions affecting more than two teeth or their surfaces, the severe form (type 4) shows the presence of two and more gangrenous roots in the maxilla intercanini sector, and the severe form with complications (type 5) shows the presence of two and more gangrenous roots in the maxilla intercanini sector with the presence of fistula and/or abscess of tooth root apex. Epidemiological data on the different ethnic groups were obtained by interviewing the parents of the examined children. The tests on significant statistical differences was performed by the variance analysis and χ2 test. Results. The prevalence of ECC in children oped 41.32 ± 8.57 months, of the South Bačka District was 30.5%. The highest disease frequency was found in Roma children (50.0%) as well as in children of Ruthenian nationality (43.8%), than in children of Slovakia nationality (37.8%), Serbian (26.1%), Hungerian (25.4%) and other nationalities (27.4%). The frequency of types 1, 3, 4, and 5 ECC was twice as high as in children who do not speak Serbian language. Conclusion. The frequency of ECC occurrence is different among ethnic groups. The highest frequency of ECC is present among the members of ethnic groups whose native language is not Serbian.