Background: Basic immunization is a mandatory immunization given to infants from birth to protect them from dangerous diseases. Complete basic immunization coverage is an essential requirement for infants. In Indonesia, immunization implementation is regulated by Law No. 17 of 2023 concerning Health and Minister of Health Regulation No. 36 of 2017 concerning Immunization Administration. Although the government is actively implementing this program, obstacles remain. Therefore, this study is needed to identify factors influencing the completeness of basic immunization in infants.Objective: This study aims to analyze factors associated with the completeness of basic immunization in infants.Methods: This study used a quantitative descriptive design with a cross-sectional approach. The study population was mothers with infants aged 0–12 months in Wotgalih Village, Jatinegara District, Tegal Regency. The sampling technique used saturated sampling. All respondents were given a questionnaire to analyze factors influencing the completeness of basic immunization in infants.Results: The study showed a significant relationship between knowledge, trust, and family support and the completeness of basic immunizations in infants. The p-value for the relationship between knowledge and immunization completeness was 0.0004; trust and immunization completeness was 0.011; and family support and immunization completeness was 0.003.Conclusion: Maternal knowledge, trust, and family support play a significant role in ensuring the completeness of basic immunizations in infants. Efforts to improve these three factors are expected to increase basic immunization coverage in the community