The digitization trend has increased dramatically in the past decade. The development of the internet and the increasing use of smartphones worldwide indicate the starting of the industrial revolution 4.0, which is now moving into a society 5.0 era. This trend has affected almost all activities of human life, including marketing, where traditional transaction processes began to shift to the digital ones. Mobile payment using Quick Response (QR) code is one of the digital transaction options in Indonesia. This study aims to investigate the key factors that encourage millennials to use the QR code in the payment process. The study focuses on four variables: mobile usefulness, trust, attitude, and behavioral intention. Trust and usefulness are often the reasons people adopt new technologies, yet the question of which one is the most influential factor for millennials arises. To answer this question, researchers surveyed 165 Indonesian millennial respondents. The results show that usefulness has a direct positive effect on using QR codes in mobile payments. Meanwhile, trust has the largest indirect effect on using QR codes through the mediation of the attitude variable.