Electrical contact resistance is an important parameter in resistance welding. In this article, a Gleeble 3500 thermal-mechanical testing machine was employed to measure the contact resistance. The machine is equipped with a special electrical resistance measuring system. The contact resistance is experimentally investigated for welding low carbon steel to themselves. A detailed work was carried out to investigate the influence of pressure, temperature on the contact resistance of low carbon steel. The experimental results show that the contact resistance decreases when pressure or temperature increases.