The paper presents an experimental study concerning the dissolution of a fixed bed of urea particles in HCl solution with the concentration 7.3, 18.25, 36.5 kg m(-3) and for the temperatures 293, 298, 303 and 308 K. In order to compare the results, the authors studied the dissolution of a fixed bed urea particles in water for the temperatures 293 and 308 K, respectively. The mean dissolution rate, the enhancement factor, the individual mass transfer coefficient and the Sherwood number were determined experimentally. Based on the results obtained, the ways were established in which temperature, concentration and fluid flow-rate influence the dissolution rate and the enhancement factor, on one side, and also the way the Reynolds and Schmidt numbers influence the Sherwood number on the other hand.