User experience is vital in usability evaluation to understand all aspects of user interactions with a product or system. The usability includes user satisfaction, efficiency, and effectiveness to achieve certain goals. On the other hand, to support the sustainability of the business, it is necessary to know the factors that significantly affect purchase intention through online travel booking application. The main aim of this paper is to investigate the usability of online travel booking system and consumer-level factors of purchase intention in online travel booking application. The research attempt to find whether product diagnosticity influences perceived quality and product trust and generally impacts purchase intention. In this study, we select an existing online travel booking application named Traveloka. The system usability scales (SUS) were used to evaluate the usability for web applications. A total of 1,225 respondents participate in online questionnaire using Google form. Most of the respondents recruited are based in Jakarta, Indonesia. The overall SUS score is only 56.13 from 100. The results show that intention for purchase is influenced by product trust and perceived quality. Moreover, the product diagnosticity (PD) supported perceived quality (PQ) and product trust (PT), and variable of product trust (PT) also supported perceived quality (PQ).