On decarburization mechanism of carbon steels and white cast irons have already studied by many investigators for varied composition. In this paper, the investigators acted decarburization treatment at 750℃for ten hours in air and studied the effect or relationship of carbon content, rolling direction and at right angle to rolling direction on decarburization of carbon steels with carbon 0.105,0.208,0.49 and 0.64% preceded by normalizing at appropriate temperature through mean of metallography. The results obtained are as follows : (1) Depth of decarburization of low carbon steels thicken more readily than high carbon steels at 750℃. (2) When carbon steels decarburize at 750℃, ferrite band become granular crystal unconcerned in carbon content. (3) When method of decarburization is the same, i seems that pre-treatment of specimens have a great influence upon depth of decarburization. (4) Depth decarburization at right angle to rolling direction thicken more readily than rolling direction.