Posyandu is a monthly routine activity designed to monitor the weight gain of toddlers by using the "Menuju Sehat" (KMS) card, providing nutrition counseling, and providing basic health services (immunization and diarrhea control). Reminder Message is a message that helps someone to remember something. Reminders can be more useful when contextual information is used to present information at the right time and in the right place. Reminder messages can be used to remind mothers of toddlers to schedule visits to their children's posyandu and increase the compliance of mothers with toddlers to posyandu. Objective: This study aims to determine the effectiveness of reminder messages on the compliance of mothers with toddlers visiting the posyandu in the working area of the Malaimsimsa Health Center Sorong City in 2021. Methods: The research design is a quasi-experimental approach with a one group pre-post test design. Sampling with purposive sampling technique, as many as 30 respondents consisting of 15 mothers and 15 toddlers. Data analysis was tested by Wilcoxon test. Results: there was an increase in the compliance of mothers toddlers to the posyandu where the p-value was 0.002 (<0.05). Conclusion: reminder messages are effective in increasing compliance with visits by mothers toddlers visit to posyandu.