Filters consisting of fibers with irregular cross-sections are commonly used ill cigarettes. However, the influence of fiber cross-sectional shape on the filter collection performance is not well understood. In the present study, the influences of fiber cross-sectional shape on both diffusional collection efficiency and pressure drop are studied both theoretically and experimentally when the fibers were placed perpendicular to the airflow. As a result, it is found that fiber cross-sectional shape and fiber orientation have little effect on the single fiber collection efficiency, but drastically change the pressure drop. The dimensionless drag force of irregular fibers is weil correlated by the width of irregular fibers projected in flow direction because the projected width of fiber determined the mutual influence of neighboring fibers. The result suggests that the use of irregular shape fiber fitter is one of the effective means to alter the pressure drop without changing collection efficiency of the filter.