Welding of high strength steels has a great risk for forming cold cracking particularly, in case of thick products and preheating is of great importance for avoiding this type of cracking. This research work focused on effect of welding process type, joint thickness, and joint size on preheating level required to avoid cold cracking of high strength steel St. 52. Both manual metal arc ((MMA) and semi-automaticmetal active gas (MAG) welding processes were used. It is found that for small size (laboratory scale) joint, cold cracking has been avoided for joint thickness up to 30mmregardless of type ofwelding process. For thicker and/or larger joint, preheating of about 150oC is necessary for avoiding cold cracking. In both cases, the recommended low hydrogen type welding electrode has been used. Cold cracking susceptibility of high strength steel is primarily related to the microstructure of the HAZ which, in turn, is related to the preheating temperature. A lower preheating level, which resulted in harder microstructure, led to increased susceptibility. Suitable preheating temperature required to prevent cold cracking increased with the increase in joint thickness and/or size. Avoiding or minimizing preheating level is of considerable importance since itwill result in reducing welding costs.