An experimental investigation with 5 kW CW CO 2 laser system was carried out to study the effects of different laser and process parameters on the microstructure and hardness of carbon steel specimen with varying carbon percentage. The laser beam is allowed to scan on the surface of the work piece varying the power (1.1-2.5 kW) and traverse speed (6-15 mm/s) at two different spot sizes using TEM 01* mode laser beam. The most hardenable microstructure achieved in case of three grades of carbon steel and the most influencing parameter on the value of hardness are reported. Besides the above study, some multipass operations are also carried out to recommend an appropriate gap between consecutive passes. © 2005 Elsevier Ltd. All rights reserved.