Objective: Mental disorder is a common complication after cardiac surgeries with cardiopulmonary bypass, and it has attracted great attention in recent years, but the exact mechanism is still unknown. Data sources: An overall retrieval for materials on mental disorders after cardiopulmonary bypass between January 1990 and December 2003 on Pubmed by using the keywords of "cardiopulmonary bypass, mental disorder, confusion, cognitive dysfunction, delirium and brain injury" in English. Study selection: Articles related to cerebral metabolism abnormality, mental states changes, cognitive dysfunction and brain injuries were chosen. Inclusive criteria: studies related to the mechanism of postoperative mental disorders after cardiopulmonary bypass. Exclusive criteria: repetitive studies. Data extraction: Totally 134 materials in volved postoperative mental disorders after cardiopulmonary bypass, 78 of which involved mental and cognitive changes, 32 involved cerebral metabolism abnormality, and 24 involved brain injuries, 108 were excluded. And 26 documents were accepted. Data synthesis: The risk factors for the mental disorders after cardiopulmonary bypass were aging, preoperative complication of hypertension and/or diabetes mellitus, cerebrovascular diseases, aortic atherosclerosis, etc. The changes of cerebral metabolism, changes of neurotransmitter, brain injuries and related genes may be involved in the pathogenesis of mental disorders after cardiopulmonary bypass. Conclusion: The mechanism of mental disorders after cardiopulmonary bypass is very complex, which involves multiple factors, and completely understanding the mechanism needs the further studies in clinical and basic researches.