Different correlations were used to predict monthly average global and diffuse radiation on a horizontal surface at Tripoli. The estimated results are then compared with the experimental data for the year 1989-1990. Using statistical tests the RMSE, MBE and MABE to evaluate these correlations, it was found that the Dogeniaux-Lemoin, and the Erbs-Klein and Duffie correlations are the best to predict the global and the diffuse radiation respectively.