In this paper, we analyze the statistical performance of several eigenspace-based adaptive array bearnformers, including conventional direct-form beamformers and generalized sidelobe canceler (GSC). It is shown that the convergence rate of eigenspace-based adaptive array beamforming depends on the number of array elements, the input signal-to-noise ratio (SNR), and the number of interferers when the desired signal is present during the weight adaptation. In contrast, the misadjostment of the array output power is a function of the number of interferers and is independent of the number of array elements when the desired signal is absent. Several simulation examples are also provided to confirm the theoretical results.