Abstract: Cinnabaris(α-HgS) is a mineral traditional Chinese material medica, as a tranquilizer and sedative, which is widely used in combination with herbs for the treatment of children high fever and convulsion.However, a large amount of mercury in Cinnabaris poses a potential risk to the immature central nervous system of children and probably causes severe memory disorders.Inthisstudy,three groups of juvenile rats were given low, medium, and high doses of Cinnabaris by oral gavage once a day for 14 continuous weeks, respectively.The blood mercury concentrations of the rats at different growth phases were monitored by atomic fluorescence spectrometry.The brain structural and functional changes related to the memory functions were investigated through HE staining and Morris water-maze test. Correlation analysis was conducted to clarify the dose- mercury exposure-toxic effect relationship of Cinnabaris and memory disorders.It was found thatthe blood mercury levels increased in both time- and dose-dependent manner.After the 14-week continuous administration of Cinnabaris, the pathological lesions in hippocampal neurons of rats in the high dose group were observed including pyknosis and disordered cell arrangement.In the Morris water-maze test, compared with the control group, rats in the high dose group exhibited the significantly prolonged latency to find the platform and the target quadrant, and the time spent in the target quadrant was obviously shortened. Thus, the significant correlations were established between Cinnabaris dose and mercury exposure,mercury exposure and memory disorders, respectively. In conclusion, the long-term and overdose administration of Cinnabaris in juvenile rats can increase the in-vivo mercury level, destroy the normal hippocampal morphological structure, and lead to memory disorders. This study provided scientific references for the potential mercury poisoning risks pharmacovigilance of Cinnabaris-containing paediatric formulations.