The GPS positioning method is widely used in the performance of forest tasks due to its convenient observation. But the result of GPS positioning without precise GPS measurements or DGPS method generally includes relatively large positioning errors. In case of mountainous regions, these positioning errors more increase because tree canopies or topographies interfere GPS satellite signals. Thus, observers have to consider how large positioning errors are included under the various observation condition in mountainous regions. In this study, we conducted a real-time GPS positioning experiment in the mountainous region with widely used three hand-held GPS measurements and a precise GPS measurement in Korea Forest Service. We observed the positioning data at various regions of topography and physiognomy. Finally, we analyzed the RMSE of each GPS positioning results under various mountain environments.