Recently, the depression of lubricity ability due to global low-sulfurization of diesel fuels gives bad effect on durability and system of fuel injection pumps. Study on lubricity of low sulfur diesel fuels is important because low sulfur regulation (less than 500ppm by mass) has been enforced in Japan in October, '97.In this study, the following subjects were investigated. Develop a Pump test for the evaluation of lubricity characteristics of diesel fuels Show what kind of bad effect the depression of lubricity of fuels would cause to fuel injection pumps. Investigate the effect of lubricity improvers. As a result, an endurance pump test using a commercial diesel engine showed the diesel fuel with severer desulfurization treatment had greatly reduced the durability of fuel injection pumps, and it became clear that such fuels would easily cause some bad effects to the control system of fuel injection timing. On the other hand, it was found that these bad effects would be improved by lowering fuel temperature at the pump inlet. Moreover, some kinds of lubricity improvers marketed could solve these problems.