To develop a passive approach for mitigating severe slugging in pipeline-riser systems, a new flow conditioner, Ωshaped pipe, had been proposed. The Ω-shaped pipe was investigated experimentally under gas-liquid two-phase stratified flow conditions in a horizontal pipeline. The effects of the geometrical parameters of Ω-shaped pipe on its flow conditioning capacity and the flow conditioning mechanism were discussed based on the experimental data. It has been demonstrated that: after the gas-liquid flow passes through the Ω-shaped pipe, the fluctuation intensity and intermittency of liquid holdup time traces increased with increasing of standard deviation, maximum value, fluctuation range, cycle time and decreasing of minimum value. The gas-liquid stratified flow regime can be converted into an intermittent flow regime by Ω-shaped pipe, the flow conditioning capacity of which becomes stronger with the increase of the radius and count of the main bent and the effect of the distance between two adjacent bents is minor. The flow conditioning mechanism of the Ω-shaped pipe can be attributed to two physical processes: liquid blocking and gas carrying-over. The outcome of this study provides a foundation for optimizing the design of Ω-shaped pipes and applying Ω-shaped pipes to mitigating severe slugging in pipeline-riser systems. 