An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the effects of strakes’ crosssection on the vortex-induced vibrations(VIV) suppression of a flexible cylinder. The square-sectioned and roundsectioned helical strakes were selected in the experimental tests. The uniform current was generated by towing the cylinder models along the tank using a towing carriage. The Reynolds number was in the range of 800–16000. The strain responses were measured by the strain gages in cross-flow(CF) and in-line(IL) directions. A modal analysis method was adopted to obtain the displacement responses using the strain signals in different measurement positions.The comparison of the experimental results among the bare cylinder, square-sectioned straked cylinder and roundsectioned straked cylinder was performed. The helical strakes can effectively reduce the strain amplitude,displacement amplitude, response frequencies and dominant modes of a flexible cylinder excited by VIV. And the mean drag coefficients of straked cylinders were approximately consistent with each other. In addition, the squaresectioned and round-sectioned strakes nearly share the similar VIV reduction behaviors. Sometimes, the strakes with round-section represent more excellent effects on the VIV suppression of response frequency than those with squaresection. An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the effects of strakes’ crosssection on the vortex-induced The square-sectioned and roundsectioned selected helical strakes were selected in the experimental tests. The uniform current was generated by towing the cylinder models along the tank using a towing carriage. The Reynolds number was in the range of 800-16000. The strain responses were measured by the strain gages in cross-flow (CF) and in-line (IL) directions. A modal analysis method was adopted to obtain the displacement responses using the strain signals in different measurement positions. The comparison of the experimental results among the bare cylinder, square-sectioned straked cylinder and roundsectioned straked cylinder was performed. The helical strakes can effectively r educe the strain amplitude, displacement amplitude, response frequencies and dominant modes of a flexible cylinder excited by VIV. And the mean drag coefficients of straked cylinders were substantially consistent with each other. In addition, the square sectioned and round-sectioned strakes nearly share the similar Sometimes, the strakes with round-section represent more excellent effects on the VIV suppression of response frequency than those with squaresection.