Micromechanical characteristics of (001) and (111) planes of gel grown pure, sodium- and lithium-doped potassium hydrogen tartrate single crystals as revealed by indentation induced technique are described. The indentation size effect (ISE) exhibited by the crystals is explained on application of proportional specimen resistance (PSR) model and the analytical law of Hays and Kendall. The load independent values of Vickers hardness of (001) and (111) planes of these crystals as indicated by indentation experiments and computed on the basis of PSR model and the analytical law are shown to be in good agreement. The doping by sodium or lithium results in the increase in hardness of potassium hydrogen tartrate crystals. The crystals exhibit hardness anisotropy. The values of yield strength of each plane of both pure and sodium and lithium doped potassium hydrogen tartrate single crystals are estimated using appropriate equations.