Dimethyl ether (DME) is one of the mast attractive alternative fuels for compression ignition engine. Its main advantage in diesel engine application is high efficiency of diesel cycle with soot free combustion though conventional fuel injection system has to be modified due to the intrinsic properties of DME. Experimental study of DME and conventional diesel spray employing a common-rail type fuel injection system with a sac type injector was performed in a high pressure chamber pressurized with nitrogen gas. ACCD camera was employed to capture time series of spray images followed by spray cone angles and penetrations of DME were characterized and compared with those of diesel. Under atmospheric pressure condition, regardless of injection pressure, spray cone angles of the DME were wider than those of diesel and penetrations were shorter due to flash boiling effect. Tip of the DME spray was formed in mushroom like shape at atmospheric chamber pressure but it was disappeared in higher chamber pressure. On the contrary, splay characteristics of the DME became similar to of diesel under 3 MPa of chamber pressure. Hole-to-hole variation of the DME spray was lower than of diesel in both atmospheric and 3 MPa chamber pressures. At 25 MPa and 40 MPa of DME injection pressures, regardless of chamber pressure, intermittent DME spray was observed. It was thought that vapor lock inside the injector was generated under the two injection pressures.