To study some informations on the morphogenesis and developmental process of the coronal suture in rats, the author performed daily oral administrations of semethylchlorotetracycline, a kind of tetracycline group, in the amount of 30mg/kg of body weight to the female rats from the 7th day of pregnaney to the time of delivery. Microscopic evaluation was undertaked on the fetal rats in the experimental group. The subject of this experiment were defined to the fetal rats of each group at 1st, 3rd, 7th and 14th day after birth. All these fetal rats were sacrificed and the heads were removed. All the tissue sections were fixed with 10% formalin, Bouin´ and Carnoy´ solution and then stained by Hematoxylin-Van Gieson stain, or Feulgen and Rossenbeck, Periodic acid Schiff, and prepared for alcian blue reaction. The results were as follows ; 1. The directions of osteogenic fibers were arranged irregulary during first 3 days, but after the 7th day they tended to change radial dirdctions like control group. 2. The density of deep stained cells by Feulgen-Rossenbeck rection were shown less in the experimental group than that in the control group in first 3 days, but there was shown no significant difference between both groups after the 7th day. 3. PAS reaction in early stage was generally negative in the experimental group unlike as in the control group, but diffuse reaction was observed in the loose middle zone like as in the control geoup agter 14th day. 4. Alcian blue reaction was negative in cambial zone, and slightly positive in uniting zone compared with control group in early stage. After 14th day, however, there was observed a tendency of moderately positive reaction.