Abstract: Detailed wind tunnel tests for a series of rectangular tall buildings were carried out. The basic characteristics of torsional fluctuating wind loads including the RMS torque coefficients and power spectral densities (PSDs) of base torque were discussed. The results show that the local RMS torque coefficients clearly demonstrate parabolic variations with the building height. The base RMS torque coefficients increase with the increase of side ratios. One obvious narrow-band peak is observed in the PSDs of base torque when the side ratio is less than 1, while two obvious peaks are found in the PSDs of base torque when the side ratio is larger than 1. The reduced frequencies corresponding to the two peaks approach to each other with the increase of side ratios. Furthermore, the formulas of the RMS torque coefficients and PSDs of base torque were also obtained by selecting the side ratio as a fitting parameter.