We conducted a study of the effects of engine technology and fuel properties on diesel exhaust gas emissions. The effect of fuel properties on exhaust gas emissions was examined using four D.I. diesel engines equipped with an oxidation catalyst, high-pressure injection, turbocharger and natural aspiration fuel charging. In addition, oxidation catalysts were installed on the two turbocharged (T/C) and natural aspirated (N/A) engines to examine their effects on reducing exhaust emissions. As a result, it was found that the installation of oxidation catalyst clearly had an effect on reducing the levels of hydrocarbons (THC), carbon monoxide (CO) and particulate matter (PM). The high-pressure injection engine was found to have a low level of PM and not be affected by the type of fuel. It was clearly shown that engine technology has a greater effect on reducing exhaust emissions than fuel properties.