LDV measurements, have been conducted to determine the in-cylinder gas flow produced by intake ports of various designs. The analysis of these measurements revealed the formation and development processes of tumble and clarified the requirements of the tumble formation by intake ports.The air flow from the intake port upper section toward the combustion chamber on the exhaust side has been found a governing factor for the increase of tumble intensity. By tuning the intake flow to have an appropriate direction in the earlier stage of the intake process, a directed flow ascending the cylinder wall is generated in the later stage of the intake process. At an early stage of the compression process, the structure of the tumbling vortex becomes clear.As an index of the tumble intensity, the instantaneous kinetic moment of air around the geometric center of in-cylinder space was proposed. It was examined that the tumble intensity at top dead center in compression stroke has already been determined by the middle of the intake process.Various intake port designs were tested to evaluate the correlation between the flow discharge coefficient and the tumbling intensity. A clear trade-off relation was observed by the conventional port design.