The effects of recirculated exhaust gas on the characteristics of NOx and soot emissions under a wide range of engine loads are experimentally investigated using a four-stroke, four-cylinder, indirect injection, water-cooled marine diesel engine operating at two engine speeds. The aim of this study is to develop the EGR control system for reducing NOx and soot emissions simultaneously in diesel engines. The EGR system is used to reduce NOx emissions. And a novel diesel soot-removal device with a cylinder-type scrubber for the experiment system is specially designed and manufactured to reduce soot contents in the recirculated exhaust gas to the intake system of the engine. It is found that NOx emissions decrease markedly, especially at higher loads, while soot emissions increase owing to the drop of intake and exhaust oxygen concentrations, and the rise of equivalence ratio as the EGR rate is elevated.