Psychological distress is prevalent among university students. However, the availability of evidence-based mental health treatment remains limited in many low- and middle-income countries, including Indonesia. Internet-delivered, mindfulness-based interventions that reduce distress have potential for treating university student distress at scale. Unfortunately, evidence-based, internet-delivered mindfulness treatments are not yet available in Indonesia. Cultural adaptation of established evidence-based, internet-delivered mindfulness interventions is needed. In this paper, we describe the process of culturally adapting an Australian internet-delivered mindfulness program (Introduction to Mindfulness) to be relevant and appropriate for treating Indonesian university students' psychological distress. To assist the cultural adaptation process, we used a systematic cultural adaptation framework and a mixed methods approach combining quantitative and qualitative methods. In study 1 (information gathering), we administered an internet-delivered questionnaire to Indonesian university students (n=248) to examine their preferences regarding an internet-delivered mindfulness intervention. In study 2 (preliminary design), a draft program was developed and independently reviewed by Indonesian stakeholders. Stakeholders (n=25) included local Indonesian mindfulness and mental health professionals (n=6) and university students (n=19), who were selected to maximize sample representativeness regarding personal and professional characteristics. To evaluate the initial design and cultural congruence of the internet-delivered mindfulness program in the Indonesian context, we conducted interviews and focus groups with stakeholders. Stakeholders also completed the Cultural Relevance Questionnaire. In study 1, most Indonesian university students (240/248, 96.8%) reported openness to an internet-delivered mindfulness program. Most of interested students (127/240, 52.9%) preferred the length of the program to be 3 to 4 sessions, with 45.8% (110/240) preferring brief lessons taking only 15 to 30 minutes to complete. They (194/240, 80.8%) recommended that the program be accessible both through websites and mobile phones. In study 2, Indonesian stakeholders generally found the internet-delivered program to be highly culturally appropriate in terms of language, concepts, context, treatment goals, and depictions of students' emotional and behavioral experiences. However, stakeholders also recommended some specific adaptations regarding the program's delivery model (eg, combining visual and audio modalities when delivering psychoeducation), cultural components (eg, including more social and spiritual activities), program practicality (eg, including rewards to promote engagement), and design elements (eg, including additional culturally relevant illustrations). Following stakeholder feedback, a new culturally adapted Indonesian internet-delivered mindfulness program called Program Intervensi Mindfulness Daring Mahasiswa Indonesia was created. This study highlights the process and importance of cultural adaptation of an evidence-based mindfulness treatment and demonstrates how this may be achieved for internet-delivered psychotherapy programs. We found that a culturally adapted internet-delivered mindfulness program was relevant for Indonesian students with some adjustments to the programs' content and delivery. Future research is now needed to evaluate the clinical benefit of this program.