Isuzu B-series engines are direct injection diesel engine comprising 4 cylinder light duty and 6 cylinder medium duty versions. These engines have been marketed on a worldwide basis not only for vehicle use but also for industrial and marine use. The production volume in 1987 was NO.1 in the world in this class.This paper describes the general outline of B-series engines and the 6BG1TC model with turbocharger and intercooler which develops the highest maximum output of these engines. This engine was developed in 1985 for the first time for medium duty truck in the domestic market and introduced in USA market in 1988. For the moment, our engineering efforts are directed to clear USA exhaust emission regulation for 1991.