The authors have investigated the effects of liquefied Dimethyl Ether (DME) mixed with conventional fuels of diesel engines. From those studies, it was clarified that DME mixing can drastically reduce unburned exhaust emissions, such as CO, HC and Particulate Matter (PM). However, the effect of sulfur content in fuels was not clearly examined. In this study, combustion analysis was carried out by varying sulfur ratio in fuels using a small size direct injection four stroke diesel engine. The test fuels were low sulfur Marine Diesel Oil (MDO, JIS A heavy oil) and MDO/DME mixed fuel. Di-t-butyl Disulfide (DBDS) was added to change the sulfur component ratio of those fuels. Experimental results obtained show that the injection duration and the specific fuel consumption increase with increasing the sulfur ratio in fuels, while the ignition delay decreases with an increase in sulfur ratio. Results also show that even though the sulfur content was increased, NOx emission and PM emission were reduced with DME mixing. It is assumed that the transfer rate of sulfur in fuel to sulfate in PM is in the range of 1.0 to 2.4% for MDO base fuel, and 0.4 to 0.9% for DME mixed fuel.