This study was conducted at Hohuanshan area, a famous alpine snow-seeing site located in central Taiwan, aiming to explore the pattern and extent of trail degradation caused by visitors' trampling impacts. Monitoring was carried out from November 2002 to October 2003. With the method of reduplicate measurement on trail transect, three trails were sampled according to the density of tramplers, and the amount of soil erosion was adopted as the indicator for impacts. The relationships between erosional impacts and tramplers' density and the environmental factors along the trails were examined. Some rudimentary conclusions are as follows: 1. The extent of trail erosion varied with the amount and density of tramplers. The soil erosion of Mt. East Hohuan Trail transect per year is as high as 161.9 cm3/cm. This figure represents the most serious extent of erosion among the three trails. The expanding rate of trail width is 6.56%. The soil erosion of Mt. West Hohuan Trail transect is 99.3 m3/cm per year and the expanding rate of trail width is only 1.52%. While on Mt. Stonegate Trail, the former figure is merely 96.5 m3/cm and the latter is 3.66%. 2. In addition to the use-level of the trails, slope and soil texture of treads are the other significant factors that affects the degree of erosion. 3. Using the changes of transect area as an indicator estimating the degree of trail erosion considerably accords with the use of Index of cover reduction (CR) and soil hardness increase (SHI). Those parameters should be the easy and practical indicator for monitoring the extent of trampling impacts in the trail management of outdoor recreation areas.