Mobile-devices are able to support a wide range of outdoor assessment activities. While there is a significant amount of research that investigates the acceptance of computer-based assessment from one side and the acceptance of mobile learning from the other, relatively few studies focus explicitly on the factors that influence the acceptance of Mobile-based Assessment. The current study implements a mobile-based outdoor educational activity in the city’s Botanic Gardens during an environmental education project. 50 secondary school students participated in a mobile-assisted assessment procedure using Quick Response (QR) - coding technology through their mobile devices. The study examines the impact of Perceived Mobility, Authentic Context and Interest/Enjoyment on students’ Perceived Usefulness, Perceived Ease of Use and Behavioral Intention to Use Mobile-based Assessment. Partial Least Squares (PLS) was used for the data analysis. Results show that Perceived Mobility, Authentic Context and Interest/Enjoyment, Perceived Usefulness and Perceived Ease of Use are all significant determinants of Behavioral Intention to Use mobile-based assessment. Furthermore, the study examines the impact of using mobile devices during the learning activity on students’ learning motivation. Implications for designing and implementing mobile-based assessment procedures are discussed.