Abstract: A strip cross-sectional element was used to suppress vortex shedding fromthin rectangular cylinders with a width to thickness ratio range B/H of 2.0~5.0 at Reynolds number Re in the range of 3.75× 10³~1.05×10⁴, where B and H are the width andthickness of the cylinder's cross-section, respectively. The cylindersurface in width is parallel to the oncoming flow. The element and thecylinder have the same length and their axes are parallel. The element'swidth is 0.5, and its thickness is small. The element's position is varied,and its main surface is perpendicular to the oncoming flow. Measurements ofwake velocities, together with smoke wire visualization, show that, vortexshedding from both sides of the cylinder is suppressed if the element isplaced at points within an effective zone, while mono-side vortex sheddingis observed if the element is applied at points within a unilateraleffective zone. The effective zone is from upstream the leading edge todownstream the trailing edge of the cylinder, and it is enclosed by theunilateral zone. The areas of the two zones increase with the growth ofB/H and decrease with the growth of Reynolds number.