Abstract: Spectral aerosol turbidity measurements over Ilorin, Nigeria acquired through ground-based Sun-sky radiometer from 340-1020nm are analyzed from April 1998-April 2006. Aerosols Optical Thickness (AOT) obtained showed a pronounced temporal trend, with maximum aerosol loading during the December-March period. Interannual variations in daily and monthly mean Angstrom exponent ( ) were also observed, resulting from differences in the bimodal aerosol size distributions. Aerosol size distribution retrievals obtained from combined solar extinction and sky irradiance measurements were also utilized in the analysis. Result shows that the fine mode particle exhibits relative stability throughout the different seasons, while the coarse fraction changes significantly. The aerosol size distributions for the December-March period yields two modes of large or coarse particles with radius near 1.71 and 3.86 �m (for December and February) or 5.06 (for January and March). Further analysis shows large differences in the asymmetric factor during 1999, 2001 and 2005 in high (Infrared) wavelengths, but relatively little changes in the short (Visible) wavelengths during the dry months of December to March.