Pressure-induced phase transformation of orthoenstatite to clinoenstatite has been studied at 7-10 GPa using a multi-anvil high pressure device with low stress (< 10 MPa) conditions. At 1000-degrees-C clinoenstatite was stabilized at pressures above 7.5 GPa. The obtained phase boundary is consistent with natural observations and previous experimental studies performed under quasi-hydrostatic condition, suggesting that clinoenstatite is a stable high pressure phase. Large differences in dP/dT slope between this result and those of earlier studies performed with piston cylinder and belt apparatus may be attributed to large differential stress in the high pressure cells of latter studies. The present study suggests that clinoenstatite can be stabilized by either hydrostatic pressure or differential stress and that the latter tends to shift the transformation boundary defined under hydrostatic condition to lower pressure.