In this paper, we have studied the solar radiation data available at two meteorological stations located in the south of Tunisia. Measurements of global solar radiation on horizontal surface are compared to predictions made by different methods. The first method is based on Angström-Prescott formula which correlates relative global solar radiation H/H0 to corresponding relative duration of bright sunshine SS/SS0. The second method, a model due to Mechlouch et al., uses cloud cover N, the hours of the day t and the quantum of the year q. The third method, an empirical relation due to Sivkov, uses the monthly sunshine duration nm and the noon altitude of the sun h. The models are compared and tested on the basis of statistical error tests (MBE, RMSE, MPE and R2) and the results are presented.