Outdoor recreation participation has increased over time and has led to environmental degradation. In Taiwan, significant increases in the number of hikers have resulted in negative effects on the natural forest environment. Therefore, this study aimed to determine the possible environmental impacts caused by hikers and to improve hikers' Leave-No-Trace (LNT) knowledge through an on-site educational program. This study adopted a two-stage approach. In the first stage, on-site observations, a questionnaire survey, and interviews were used to assess the impacts of hikers on the natural environment. Then, an LNT educational program was implemented and evaluated. The results indicate that hikers regard air quality and wild animal issues as the factors most affected by hiking. The results of the second stage revealed that the individual and total scores for the knowledge of the seven LNT principles significantly increased between the pretest and the post-test. Managerial implications and suggestions for future research are proposed on the basis of the obtained results.