Abstract: In this paper, we describe an automatic people-counting system based on a wireless sensor network at a mountain area. Several people-counting systems have been proposed separately. However, these systems are not suitable to a place such as the mountain area because of a few problems. In this paper, we develop a system which can count the number of visiting people and sense environment information to protect an ecosystem of the mountain area. For people-counting in the mountain area, our system uses two photo-beam sensors, a big rechargeable power and a solar power. Our people-counting method can automatically count the number of incoming and outgoing people at a special point in real time. Moreover, the environment sensors measure environment information at the mountain area, and constitute the wireless sensor network with photo-beam sensors. To establish this system in Korea Mountain, we did tests on the wireless communications range and the reliability of people counting. By the testing results, we found that the developed system is suitable within 200 meters for effective wireless communications in Korea Mountain. When the width of a path up a mountain is within 1.5m, the reliability of people-counting in our system is over 90%. The number of visiting people and the measured environment information are used to manage and control the mountain.