The possibility of wear reduction to the injector needle and of fuel rduction leakage from the injector is examined by using fatty acids and polymer type additives. The newly developed wear test equipment is used because of the implementation of an actual injector and DME as a fuel. A HFRR (High Frequency Reciprocating Rig) is also used to select a suitable concentration of additive. In this case, ETBE is used as a fuel instead of DME because of the similar SP value of DME. The concentration of fatty acids at around 300 ppm satisfies the recommended value (WSD<460μm) for diesel fuel. However there is some wear at the needle tip despite no evidence of wear at needle guiede. Therefore, the blend of fatty acid and polymer type additives is used to improve the wear resistance and increase the viscosity of DME to prevent a leam from the injector. As a result, the blend additives are effective for reducing wear at the needle tip and decreaing the possibility of leakage to almost nothing from the injector.