The present study aims at evaluating the performance of wind speed sensors installed at different heights on a 40 m tall wind mast during a period of 33 months between July 01, 2006 and April 01, 2009. The performance has been evaluated by estimating the tower distortion factor (TDF), scatter factor (SCF), and studying the correlation ship between the co-located wind speed sensors. A total of 23,730 hourly mean wind speed records were used to evaluate each sensor. The overall values of TDF between wind speed sensors WS5/WS6 at 40 m and WS3/WS4 at 30 m were found to be 0.025 and 0.021 without tower shading and 0.047 and 0.035 with tower shading. The study showed that the performance of sensors did not deteriorate with time rather lower values of TDF were obtained with passage of time. At 40 m AGL for wind speed sensor WS5 the tower shading effect was pronounced (>1) within wind direction range of WD2 from 169° to 195° and in case of wind speed sensor WS6, the tower shading effect of <1 was evident from WD2 of 240° to 270°. More or less the same type of observations was noticed for wind speed sensors WS3 and WS4 at 30 m AGL. The SCF values were higher for wind speed sensor at 40 m compared to those at 30 m AGL.