A high number of people with mental disorders are in low- and middle-income countries (LMICs, including Indonesia) and they do not receive adequate treatment due to low service utilisation, evidence on factors impacting utilisation is inconsistent. This empirical study aimed to understand this phenomenon better by exploring mental health service use among Indonesian adults and identified contributing factors. A non-random-self-selection-sampling online survey was carried out between May and June 2021 including questions for service utilisation and potential factors affecting it. The participant inclusion criteria were Indonesian, aged 18 or older, and living in Indonesia. The measure used standardized questionnaires (i.e. Perceived Helpfulness of Interventions) and hierarchical logistic regression was used for statistical analysis. Out of 5,211 participants, only about 26.5% used mental health services in the past three years. Significant predicting factors (p < 0.001) including perceived helpfulness on the services (OR 2.82), disability status (OR 2.72), and adequate insurance literacy (OR 1.91). Based on these findings, suggestions for improving health financing and social health equity for future access to in Indonesia were recommended, such as the importance of expanding insurance coverage and the necessity to improve awareness of mental health services.