The ultrasonic guided wave phased array technique offers an efficient means to interrogate damages in plate-like structures. When applying this technique to multilayer composite plates, however, the anisotropic behavior of the composite materials leads to significant influences on the beam steering performances of the phased arrays. This paper investigates the beam steering performances of guided wave phased arrays for multilayer composite plates in terms of phased array directivity profiles under influences of anisotropy. Angular dependences of guided wave amplitudes and phase variations in composite plates obtained through a Green's function based method are implemented into directivity profile calculations to account for the influences of anisotropy in a quantitative way. Guided wave phased array experiments are carried out to validate the directivity profile calculations.