This paper studies the observer-based bounded tracking control problem of second-order multi-agent systems in a disturbance environment via sampled-data control. Two sampled-data protocols are introduced under the assumption that the dynamic leader is only available to a portion of agents and distributed observers are designed to estimate the velocity of the active leader. For the fixed communication topology case, necessary and sufficient conditions of bounded consensus tracking are obtained by using the matrix analysis method. For the switching communication topology case, we prove that system can achieve bounded tracking by applying the common Lyapunov function and perturbation theory. Simulation examples are given to illustrate the effectiveness of our results.