The mechanical properties of solution grown potassium sodium hydroxide borate hydrate single crystal (KSB) have been obtained by using Vickers microhardness studies in the load range from 10 to 70 g. The variation of microhardness with load represents the load independent value of hardness (Indentation size effect). The meyer's index number ‘n’ is calculated as 1.81 and it belongs to soft material category. Various mechanical parameters such as yield strength, elastic stiffness constant, fracture toughness, brittleness index, hardness contour and crack propagation of KSB single crystal are discussed in detail. © 2017 Elsevier B.V.