We report on a measurement of the mean charged-particle multiplicity of jets in dijet events with dijet masses in the range 80–630GeV/c2, produced at the Tevatron in pp¯ collisions with s√=1.8TeV and recorded by the Collider Detector at Fermilab. The data are fit to perturbative-QCD calculations carried out in the framework of the modified leading log approximation and the hypothesis of local parton-hadron duality. The fit yields values for two parameters in that framework: the ratio of parton multiplicities in gluon and quark jets, r≡Ng-jetpartons/Nq-jetpartons=1.7±0.3, and the ratio of the number of charged hadrons to the number of partons in a jet, KchargedLPHD≡Nchargedhadrons/Npartons=0.57±0.11.