An explicit form of the Mueller matrix is given for an anisotropic sphere fulfilling the requirements of the Rayleigh-Gans-Debye (RGD) approximation. The angular dependences of single matrix elements are compared with Lorenz-Mie predictions for an isotropic sphere. Good agreement between the Lorenz-Mie model and that of RGD is observed where the latter is applicable. The magnitude and sign of the matrix elements depend on the size parameter kR (k = 2pi/lambda;R is the radius of the sphere) as well as on the magnitude and sign of the (ñ - 1)/Deltan parameter, where ñ is the relative refractive index and Deltan is the relative anisotropy of the sphere.