In this paper, we present a chaos-based decoupled multiuser ranging (DEMR) estimator for multiuser DS-UWB ranging system. In the DEMR estimator, users are decoupled by the knowledge of all the users' limited number of data bits. Then, the ranging performance of each user mainly depends on the non-cyclic autocorrelation property of the spreading code. Based on this property, we improve DEMR estimator by using the selected binary chaotic sequences instead of the Gold sequences in order to increase the system capacity and to improve the ranging accuracy. Simulations in CM1 channel show that the chaos-based DEMR estimator is quite near-far resistant and achieves a noticeable ranging accuracy even in a heavily loaded system. Compared with using Gold sequences, chaos-based DEMR not only works with more users than full load of Gold sequences but also improves the ranging accuracy especially under low SNR condition.