The highly efficient nonlinear optical (NLO) crystals, 4-dimethylamino- N -methyl 4 stilbazolium tosylate (DAST) crystals, have been grown by the slope nucleation technique (SNT) and the new derivative in the same family, 4-ethoxy benzaldehyde- N -methyl 4 stilbazolium tosylate (EBST) crystals by slow evaporation technique. In this present work the mechanical, dielectric studies and surface analysis of EBST and DAST were compared. The Meyer's index number ( n ), fracture toughness and brittle index were calculated using Vicker's microhardness number. Young's modulus was calculated using the Knoop hardness value. The surfaces of the grown crystals were analyzed with etching. The etching was done using methanol as solvent. The dc conductivity was calculated from the dielectric study by the cole–cole plot method. The dielectric constant and dielectric loss were found to decreased when the frequency increased.