Soil compaction caused by tractor traffic is one of the most important factors responsible for environmental degradation and leads to plant yields reduction. It is a serious problem for perennial crops, where the soil is wheeled and compacted without ever being loosened. The aim of this study was to evaluate the effect of tractor traffic on tall fescue (Festuca arundinacea) yields and roots development. The field experiment was located in Mydlniki near Cracow, Poland, on silty loam Mollic Fluvisol. Experimental plots were established in completely randomised design with four replications. Four compaction treatments were applied using the following range of number of passes: (P0) untreated control, (P2) two passes, (P4) four passes and (P6) six passes completely covering plots surface after each harvest. The dry matter (DM) of the yield and roots (RMD) were determined. Morphometric parameters of roots were estimated using image analysis software, and root length density (RLD), specific root length (SRL) and mean diameter (MD) were calculated. Bulk density of soil under perennial grass was increased with increase in the number of tractor passes. The tractor traffic resulted in significant decrease in tall fescue annual yields. However, this effect was not observed during the first cut, when the yields were equal for all the treatments. The soil compaction caused by multiple tractor passes changed the morphology and distribution of roots. More roots were found at compacted objects (RLD above 40 cm cm-3 at P4 treatment) with respect to untreated control, P0 (26 cm cm-3). These roots were also significantly thicker. The MD value ranged from 0.44 mm at P4 treatment to 0.31 mm at P0.