Objective To investigate the stimulation of Cinnamaldehyde to the pulp tissue and the periapical tissue of rats′teeth, to provide evidence for developing Cinnamaldehyde as a pulp- cap of pulpotomy in primary teeth. Methods Using Cinnamaldehyde as pulp- cap in pulpotomy of rats′teeth, set up Cinnamaldehyde group, formaldehyde cresol formocresol group and blank group. After different treatment according to the empirical procedure, rats were killed in the 4th week and on the 12th week. Then the experiment teeth and the periodontal tissue were made into HE slides and observed using light microscope. Results The 4th week，internal absorption, external absorption, and calcification were of no significance among all the groups. Inflammation in blank group was far more severe than that in other two groups（P
