An elevator group control system for controlling multiple elevators cars each of which serves a plurality of floors includes a route preparation section which, at a time of assigning a hall call to one of the elevator cars, calculates a future trajectory for each of the elevator cars. The future trajectory for each elevator is for a case in which the hall call is assigned to the elevator car. A selecting unit which determines a selected one of the elevator cars to which the hall call is to be assigned using the calculated future trajectories.