In recent years, the interior noise has been required not only to reduce the sound pressure level, but also to improve the sound quality, especially during acceleration. This paper describes the development of engine sound quality for the new model `ARISTO (GS300)` with in-line 6 gasoline engine. We used the sound simulator in order to evaluate the engine sound quality during acceleration, and decided the target sound. To attain that sound, the light-weighed Piston and connecting rod, and the improvement of intake system are adopted. 7 refs., 13 figs.