Worldwide concern about combustion chamber deposits (CCDs) has increased from the viewpoint of fuel and additives technology, which has been developed for the cleaning of intake valve deposits (IVDs), intake port deposits and injector deposits. The research effort described here, focused on the differences between CCDs and IVDs in terms of quality based on analyses of CCDs and IVDs collected from used vehicles from the Japanese market. The CCDs and IVDs were characterized according to weight, benzene-solubles and sulfated ash. Since the sulfated ash in CCDs is a key to understanding the effect of engine oil on CCD formation, the relationship between CCDs and the sulfated ash in CCDs was evaluated under the two typical conditions on a 2.0L engine testing bench. Based on the results, the gasoline-related and oil-related factors were estimated for these conditions. Moreover, the effect of CCDs on exhaust emissions was investigated in a 2.2L vehicle. The engine-out and tailpipe emissions in the Japanese 10.15 mode were measured during a mileage accumulation test for 50,000 km on chassis dynamometers. After 50,000 km, the CCDs were removed with a walnut shell blaster, without disassembly of the engine, and the emissions were again measured. Consequently, the CO and NOx in the engine-out and tailpipe emissions were increased by the CCDs, while HC emissions were affected little by the CCDs.