In the case of a rectangular prism with a side ratio of less than 0.5 and D-section (semi-circle) prism, the low-speed galloping appears at lower reduced velocity than the resonant reduced velocity. In this paper, we carried out free-vibration tests of cantilevered rectangular prisms with the side ratio under 0.5 and D-section (semi-circle) prism in a water tunnel. The effects of the side ratio and the turbulence intensity of free-stream on the flow-induced vibration characteristics of prisms were investigated. The response amplitude of a rectangular prism increases with decreasing of the side ratio. The D-section prism vibrates at lower reduced velocity than the rectangular prism with a side ratio of 0.5, which has the same depth as the D-section prism. It is found that the free-vibration characteristics of rectangular and D-section prisms are influenced by high turbulence of the free-stream.