In this study, we proposed an augmented reality- (AR-) based mobile touring system for an authentic learning activity, which enables students to observe and learn key information regarding cultural heritage sites. To evaluate the effectiveness of the proposed system, we conducted an experiment in a cultural heritage course at a Taiwanese university. A total of 72 students were divided into two groups and randomly assigned to an experimental group who learned with the AR-based mobile touring system and a control group who learned with a conventional mobile touring system. The experimental results show that the AR-based mobile touring system significantly improved the students' memorising dimension of learning achievement, as compared with a conventional mobile touring system. Moreover, the positive impact of the proposed system on students' actualised interest and task-based interest factors provide a particularly encouraging result for outdoor experiences. These experimental results also suggest the potential of AR technology to increase students' learning interest and improve their learning achievements in outdoor settings. Therefore, we suggest that, when applying an AR-based mobile touring system in authentic learning activities, AR virtual objects should be designed appropriately, in order that the content recall performance and learning interest are enhanced.