Much research has been conducted to study the size-dependency of material properties, as can be found from the open literature. Recent results on combined size, rate and thermal effects further demonstrate the dominant influence of specimen size on material strength, as compared with the loading rate and thermal effects. However, little has been done to understand the loading history and crystal orientation effects on the size-dependency of material properties. To evaluate the safety and integrity of MEMS devices under general loading conditions, a series of molecular dynamics simulations are performed to investigate the size-dependency of single crystal diamond properties with various crystal orientations under shear/tension and tension/shear loading conditions. It appears from the preliminary findings that the loading history and crystal orientation do have certain influence on the size-dependency of material properties. Specifically, the failure pattern is insensitive to the loading history, which provides useful information for formulating a multi-scale material model under general loading conditions.