The disturbance observer (DOB) is widely used in high precision motion control applications as an effective means of rejecting disturbances. DOB design essentially boils down to the design of the Q filter. In traditional DOB design, the Q filter follows a standard form such as the Butterworth or binomial, where the bandwidth is the only tunable parameter. In this paper, we employ a more general form of Q filter, and tune the parameters iteratively using a data-based approach according to some design criterion. Simulation results show that the data-based design achieve improved disturbance rejection in low frequency region while the high frequency noise attenuation and robust stability is not compromised.