Vickers microhardness study was carried out on the (110) face of the gel-grown cadmium mercury thiocyanate (CMTC) single crystal, subjected to the loads 10, 25 and 50 g. The measurements were made at room temperature with the indentation time as 10 s. Vickers hardness number Hv was calculated and it is found to increase with the applied load. Mayer's index number 'n' and elastic stiffness constant were calculated. The anisotropy of the crystal is also studied. The results are discussed in detail. © 2007 Elsevier B.V. All rights reserved.