The results of oxidative leaching kinetics of sphalerite concentrate in ammonia solution are presented. The effect of oxygen partial pressure (0.5-10 atm), ammonia concentration (1.54-5.35 M), pH (10.4-11.2), leaching temperature (90-130 degreesC), particle size (-90+75 to -53+45 mum), and agitation speed on the leaching rate were determined. For the generation of kinetic data, 1% of slurry density was used. Leaching rate was nearly independent of agitation and pH in the studied range. From the comparison of experimental reaction rate constant with calculated mass transfer coefficients, it was established that chemical reaction rate is the slowest process. Shrinking core model for surface reaction fitted the experimental data as well. Reaction order with respect to P-O2 and [NH3] were 0.2 and 0.6, and the activation energy was determined to be 44.3 kJ/mol. (C) 2002 Elsevier Science B.V. All rights reserved.