The mechanical and thermal properties of single crystals of the type-I clathrate compounds Ba(8)Ga(16)Ge(30) and Sr(8)Ga(16)Ge(30) have been investigated by measuring the elastic constants, coefficients of thermal expansion (CTE) and plastic deformation behavior in compression. The feasibility of these two clathrate compounds as a thermoelectric material in terms of mechanical stability under possible thermal stresses is evaluated by calculating thermal stresses that are expected to develop within these compounds when used as thermoelectric devises.