Mason’s nonlinearity constantsD[W. P. Mason, inPhysicalAcoustics, edited by W. P. Mason (Academic, New York, 1965), Vol. IIIB, Chap. VI] in GaAs at 298 K have been estimated from second‐ and third‐order elastic constants along the [100], [110], and [111] directions for longitudinal and shear waves. These values are further used to estimate the frequency dependence of the ultrasonic attenuation in the range 40–640 MHz and are found to be in good agreement when compared with experimental values available in the literature. Previously, it was established that phonon‐phonon interactions produce a drag on moving dislocations in a solid. In the present work, the drag coefficients for edge and screw dislocations along the [100] and [110] directions in single‐crystal GaAs have been estimated from the evaluated nonlinearity constantDvalues at 298 K. We have also estimated the values of Breazeale’s nonlinearity parameters &bgr; [M. A. Breazeale and J. Philip, inPhysicalAcoustics, edited by W. P. Mason and R. N. Thurston (Academic, New York, 1984), Vol. XVII, Chap. I] along the [100], [110], and [111] directions and found them to be consistent for the three principal orientations, compared with the results for other samples. It is pertinent to note that the mode Gru¨neisen number &ggr; jiinvolved in the estimation of Mason’s nonlinearity constantDis deceptively similar to Breazeale’s nonlinearity parameter &bgr;. The nonlinearity constantDis evaluated from knowledge of the Gru¨neisen number &ggr; jifor various modes and directions, whereas Breazeale’s nonlinearity parameter &bgr; is the negative ratio of coefficients of nonlinear term to the linear term of the (dissipationless) nonlinear wave equation for pure mode directions. BothDand &bgr;, in general, are temperature dependent.