The hardness of NaCl crystal in the presence of mono, divalent and polyvalent ions were measured. Measurements were made in the indentation load range from 5x10(-3) to 20x10(-3) N. The measured data showed that there is an indentation size effect. Classical Meyer's law was used for the characterization of, crystal hardness of NaCl. The Meyer index was found to be smaller than 2 indicating brittle material characteristic. The PRS model was also used for the determination of the load-independent microhardness value. It was found that the crystal hardness of NaCl is chancing depending on the type of impurity and the concentration.