Objectives: As the number of migrant children in South Korea has increased, oral health disparities have become more pronounced. This study aimed to examine the association between oral health behaviors and the Simplified Oral Hygiene Index (OHI-S) in children with a migrant background. Methods: A cross-sectional survey was conducted among 99 children with a migrant background residing in South Korea. Data were collected using structured questionnaires and oral examinations. Descriptive statistics, t-tests, ANOVA, and multiple linear regression were performed to analyze the relationship between oral health behaviors and OHI-S scores. Results: The mean OHI-S score was 4.16±1.29, indicating generally poor oral hygiene. Children who brushed their teeth ≤3 times/day had significantly higher OHI-S scores (B=1.808, p<0.001). Frequent consumption of sticky or sugary snacks was also associated with higher OHI-S scores (once/day: B=1.839; ≥2 times/day: B=2.124; both p<0.001). In contrast, unmet dental care needs and sweetened beverage intake were not significantly associated with OHI-S scores. The final regression model explained approximately 59.3% of the variance in OHI-S (adjusted R²=0.593, F=16.661, p<0.001). Conclusion: Oral health behaviors, particularly tooth brushing frequency and snack consumption, significantly influence oral hygiene among children with a migrant background. Tailored oral health education and dietary interventions are required to promote oral health equity in this population.