Topographic influence on vegetation indices (Vis) is an inevitable issue and usually neglected in their large scale applications. In this study, the topographic effects on SR (simple ratio), NDVI (normalized difference vegetation index), RSR (reduced simple ratio), MNDVI (modified normalized difference vegetation index), and MAVI (moisture adjusted vegetation index) derived from Landsat TM data over a mountainous forest area are evaluated. Two simple methods, the cosine correction and c-correction models, with different treatments of the influence of the diffuse irradiance on reflectance, are used to remove the topographic effects on the selected Vis. The results indicate that the topography affects strongly vegetation indices which are not expressed as band ratios, such as RSR and MNDVI, resulting in negative biases on sun-facing slopes and positive biases on sun-backing slopes. As the slope increases, these biases increase rapidly. Therefore, the topographic effects should be removed before using these non-band-ratio vegetation indices for vegetation parameter retrieval. Vegetation indices which can be expressed as band ratios, such as SR, NDVI, MAVI, can greatly reduce the noise caused by topographical variations. However, these indices still include significant topographic effects on steep slopes. SR is more sensitive to topographical variations on steep slopes than NDVI and MAVI, because the reflectances in the near infrared (NIR) and shortwave infrared (SWIR) bands are more sensitive to topographical variations than that in the red band. Diffuse radiance from the sky in the red band can moderates the variations of red band reflectance with topography, while this moderation is absent in the NIR and SWIR bands. The c-correction model is much better than the cosine correction model in removing topographic effects on Vis, especially on steep slopes.