The accurate mapping of chromatic-dispersion distribution along single-mode optical fibers with the best spatial resolution ever reported is experimentally demonstrated. The method consists of a new way of probing four-wave-mixing (FWM) efficiency along the fiber using Brillouin-optical-time-domain analysis (BOTDA). The new setup eliminates many noise problems found in previous configurations, allowing a tenfold improvement in the spatial resolution of this kind of measurements. Resolutions of 20 m in a 1.1-km standard fiber and 150 m in a 6.7-km dispersion-shifted fiber (DSF), respectively, were achieved. © 2005 IEEE.