This study aims to examine and describe the factors that influenced the National Health Insurance System (NHIS) enrolment and discusses a possible policy improvement to assist Universal Health Coverage (UHC) implementation in Indonesia by conducting a systematic review. Using PRISMA guidelines, 21 articles are included in the analysis. To sum up, two main factors identified that affected the low enrolment of the NHIS include socio-demographic and health-related, and other factors. The government may consider the factors and suggested policy discussed in the study to improve population coverage and reach Universal Health Coverage goal.