A new series of 15.2 liter heavy duty diesel engine has been developed and launched into production by Komatsu Ltd. The in-line 6 cylinder direct injection engine covers the power range of 184 - 368 KW (250-500PS) for versatile applications. It is characterized by extremely low fuel consumption (minimum b.s.f.c. is 189 g/KW.h), low noise and good transient performance, which were achieved by various design features such as ductile cast iron pistons, unique intake port arrangement and underframe construction. Turbocharged and turbocharged aftercooled versions are currently available, however, higher output versions incorporating air-to-air aftercooling or two-stage turbocharging are being developed.This paper describes details of the development objectives and the design features of the S(A)6D140 engines.