Aerodynamic damping ratios play an important role in the estimations of wind-induced responses of modern super-tall and slender buildings and structures. In the present study, along- and across-wind aerodynamic damping ratios of a square cross-sectional conventional and tapered super-tall buildings with height of 448m were investigated using the Random Decrement Technique (RDT) for the responses obtained from the aeroelastic wind tunnel tests. Wind tunnel tests were conducted under the urban flow condition. Effects of building shape, normalized velocity and wind direction on aerodynamic damping ratios were comprehensively discussed. It was found that the along-wind aeroelastic aerodynamic damping ratios show similar linear increasing trends on the normalized velocities at small wind directions regardless of building shapes. But the across-wind aerodynamic damping ratios show clear differences depending on building shapes, showing different peaks and different normalized velocities at which peaks of aerodynamic damping ratios occur and positive aerodynamic damping ratios become negative. Lastly the effect of trigging value in RDT on aerodynamic damping ratios was examined by changing it from one standard deviation to three times of standard deviation. By enlarging the trigging value, the differences in aerodynamic damping ratios increase, implying the optimal trigging values may exist between one standard deviation and ${sqrt{2}}$ times of standard deviations in the current experimental conditions.