A new chip breaker was investigated experimentally in order to find out a more effective chip breaker than the commercial chip breaker in turning. It was found that this chip breaker was almost effective for SS400, SCM440, S55C, SUS304, SK5 under the cutting condition of the depth of cut 0.1 to 3.0mm and the feed rate 0.05 to 0.51mm/rev. However, the plastic deformation of the nose corner on the insert occurred under the cutting condition of large depth of cut and high feed rate, especially for SCM440. This seems to be caused by the rise of cutting temperature.So, in order to cool the insert, the water-soluble cutting fluid was used. In wet cutting, the effectiveness of this chip breaker was improved. The principal and feed cutting forces in wet cutting were a little greater than that of dry cutting under a small depth of cut, but became slightly less under large depth of cut. The effectiveness of chip breaking of this chip breaker was kept up to the width of the flank wear 0.2mm in wet cutting. In wet cutting, the plastic deformation of the nose corner was reduced.