This study examined the effects of laser heat treatment of work material on chip breakablity and surface roughness in turning of carbon steel. A direct diode laser (DDL) was installed on the tool post of a CNC lathe, and the laser was used to linearly irradiate the cylindrical workpiece surface in the longitudinal direction prior to the turning test. P30 grade carbide and TiC-Al₂O₃ ceramic tools were chosen and a breaker piece was used in each insert. In the case of ordinary turning without laser heat treatment, the chip was broken at a high feed rate and low cutting speed. Laser heat treatment, however, made it possible to break chips over a wide range of cutting conditions because the work material was partially embrittled. The surface roughness was somewhat reduced due to the removal of adhesive objects on the cutting edge by intermittent cutting of selective hard-brittle materials.