In the V-belt drive system, temperature and humidity are the most effective parameters affecting the slippage. This study is done in two stages. Firstly, experimental study has been carried out and the effect of temperature, relative humidity on the slippage between V-belt and pulley has been analyzed. At the second stage, non-linear regression analysis has been carried out to act a prediction equation for determining of friction coefficient between V-belt and pulley at the different temperature and humidity. In the analysis MATLAB Statistics Toolbox was used. At the result of the analysis the prediction equation has been obtained with 0.995 correlation coefficient. It has been seen that increase of temperature and humidity leads to decrease in the coefficient of friction (slippage raises). In high humidity conditions, slip quantity raises rapidly when temperature is 60-80 degrees C.