The load dependence of apparent microhardness of beta-Sn single crystals having different growth directions is investigated. The measurements are performed on (110) planes of these crystals in the load range from 10 to 50 mN. It is found that the degree of the microhardness anisotropy decreases for higher indentation test loads. The examined materials exhibit the behaviour of indentation size effect (ISE), i.e., the apparent hardness increases with decreasing indentation load. Neither Meyer's law nor the proportional specimen resistance (PSR) model can fully explain the nonlinear variation of microhardness with load. Instead, preference is given to modified the PSR model based on the consideration of the effect of machining-induced residually stressed surface on the hardness measurement.