This Shop Manual covers the Komatsu PC300-6, PC300LC-6, PC350-6, and PC350LC-6 hydraulic excavators, specifically for models with serial numbers PC300 series 33001 and up, and PC350 series 12001 and up. These excavators are engineered for demanding construction and earthmoving applications, featuring robust construction and reliable performance. The "-6" generation signifies advancements in their design and operational capabilities, ensuring efficiency and durability in various work environments. This comprehensive manual provides detailed information essential for the maintenance and repair of these Komatsu hydraulic excavators. It includes explanations of component structure and function, pre- and post-repair checks, adjustment procedures, and troubleshooting charts. Furthermore, it outlines disassembly and assembly processes, maintenance standards for inspected parts, and includes hydraulic and electric circuit diagrams. This resource is invaluable for owners, mechanics, and technicians seeking to maintain optimal performance and longevity of their equipment.