An experimental study of cesium resonance exchange collision, Cs(6P(3/2), v) + Cs(6S(1/2), v')-->Cs(6S(1/2), v) + Cs (6P(3/2), v'), was carried out. Populations of excited atoms that all have the same z component of velocity were produced by pumping a vapor with a narrow-band laser. A counterpropagating single-mode diode laser was used to probe the excited atom velocity distribution in the 6P(3/2)-->8S(1/2) transition. Fluorescence was monitored in the 8S(1/2)-->6P(3/2) transition. The magnitude of the thermalizinng effect of resonance exchange collisions was estimated by measuring the ratio of the intensity in the narrow features to that associated with the Doppler pedestals. The rate coefficient of 9.62 x 10(-7) cm3 x s(-1) for the resonance exchange collisions was yielded. This work demonstrates that, in a pure metal vapor, the thermalization of velocity-selected excited-atom distribution by the mechanism of resonance exchange can be three orders of magnitude greater than that from velocity-changing collisions.