In this study, influence of several formulation factors on the release kinetics of potassium chloride from directly compressed matrices are investigated. Formulations containing hydrophilic (methylcellulose, carbomer), plastic (polyvinyl chloride), and wax (glycerol palmitostearate) matrix materials at concentrations of 10, 15 and 20%, incorporated with potassium chloride as active ingredient and insoluble excipients were prepared and studied in vitro using the USP XXI/NF XVI rotating paddle method. Hardness had no markedly effect on the release characteristics of formulations except for wax matrix material formulation. Results of goodness of fit analysis applied to release data had shown that the release mechanism was described by the Higuchi diffusion controlled model. Positive deviations from Higuchi equation might be due to the erosion of gel layer. Analysis of in vitro release mechanisms indicated that the most suitable results were obtained by methylcellulose and glycerol palmitostearate.