PurposeVaccine-preventable diseases have decreased globally. However, measles and diphtheria outbreaks still occur in Southern Thailand, where Muslims are predominant with a documented low vaccine coverage. The purpose of this study was to investigate Muslim parents’ beliefs and factors influencing them to complete immunization of children aged 0–5 years in Y.L. province, Thailand.MethodA descriptive qualitative study was conducted, using focus group discussion with 26 participants. They are parents whose children had complete or incomplete vaccination and community/religious leaders. Data were analyzed using content-analysis and triangulation method was used to ensure trustworthiness.ResultsFour major themes emerged from the analysis: (1) positive vaccine beliefs, which included knowledge and awareness of vaccination, trust in vaccine efficacy, and religious beliefs; (2) positive factors influencing positive beliefs and vaccine acceptance, which were accessibility of reliable sources, and imitation of leaders and health-community-network; (3) negative vaccine beliefs, including bias in vaccine efficacy and safety, personal beliefs about sources of vaccines, and religious misconceptions regarding the value of vaccines and Halal concerns; and (4) negative factors influencing negative beliefs and refusal of vaccination, which were perception of disadvantages of vaccines spread by word-of-mouth, trust in person over empirical evidence, religious views based on self-interpretation, and lack of public information on Halal vaccines.ConclusionBoth positive and negative factors influencing complete immunization were found in this study. To enhance vaccine acceptance, health care providers should understand Muslim cultural beliefs by offering parents a chance to express their attitudes and encourage vaccination via religious leaders and community role models.