Sound intensity based active control for the reduction of sound radiated out of the duct exit is studied experimentally as well as theoretically. The active intensity control strategy is derived based on the relation of the exterior sound field out of the duct exit and interior sound field of the duct. One of the features of the active intensity control strategy is that the control performance can be maintained regardless of the sensor location, compared with the conventional local sound-pressure control methods at either interior downstream or exterior field position. Simple numerical examples are demonstrated to compare the acoustic characteristics of the active intensity control scheme with the other control strategies. For a more practical comparison with the conventional sound-pressure control strategy, an experiment, based on a time-domain adaptive filtering with an intensity sensor filtered-x LMP (least-mean-product) algorithm, is performed. From the experimental results, it is shown that the exterior sound field is much more observable by sensing the active intensity than by sensing the sound pressure. It is also demonstrated that the active intensity control performances are superior to the sound-pressure control ones.