In this paper we study thermalization in a strongly coupled system via AdS/CFT.Initially, the energy is injected into the system by turning on a spatially homogenous scalar source coupled to a marginal composite operator. The thermalization process is studied by numerically solving Einstein's equations coupled to a massless scalar field in the Poincare patch of AdS 5 . We define a thermalization time t T on the AdS side, which has an interpretation in terms of a spacelike Wilson loop W (l ≃ 1 T ) in CFT. Here T is the thermal equilibrium temperature. We study both cases with the source turned on in short(∆t T . In the latter case, we find double-and multiple-collapse solutions, which may be interpreted as the gravity duals of two-or multi-stage thermalization in CFT.In all the cases our results indicate that such a strongly coupled system thermalizes in a typical time scale t T ≃ O(1)