This paper describes the measurement and analysis of the gas flow characteristics in the combustion chamber, which have an important effect on the combustion process. A laser Doppler velocimeter (LDV) was used to measure gas behavior in the combustion chamber under motor-driven operation. The flow patterns at the center of the combustion chamber are obtained first. In order to investigate the influence of engine variables such as speed and combustion chamber shape on the in-cylinder flows, the two components (U, V) of mean velocity and velocity vectors are determined at given crank angles for various speeds and for two shapes of the combustion chamber. In addition, velocity vectors at several radial locations in the combustion chamber show the in-cylinder flow characteristics of the two-stroke S. I. engine.