Abstract： Objective To observe the effect of hippocampal protection on cognitive dysfunction of localized small cell lung cancer patients undergoing prophylactic cranial irradiation(PCI).Methods A total of 81 patients with localized small cell lung cancer from Linyi Cancer Hospital from January 2017 to February 2021 were collected.The patients were divided into two groups according to whether hippocampal protection was performed during PCI,41 cases in the observation group was with hippocampal protection and 41 cases in the control group was without hippocampal protection.The neurocognitive function,the activities of daily living,adverse reactions and survival rate of the two groups before and after treatment were compared.Results There was no statistically significant difference in MoCA scores before radiotherapy between the two groups(P>0.05).3,6 and 12 months after radiotherapy,the MoCA scores of the two groups were lower than those before treatment,and the observation group was higher than that of the control group(P<0.05).ADL scores of the two groups decreased after radiotherapy and patients were mild dysfunction 3 and 6 months after radiotherapy(P<0.05),but there was no statistically significant difference between the two groups(P>0.05).12 months after radiotherapy,the ADL score of the observation group was significantly higher than that of the control group(P<0.05).There were no significant differences in adverse reaction,2-year brain metastasis rate and survival rate between the two groups(P>0.05).Conclusion The application of hippocampal protection technology in PCI treatment can improve the neurocognitive function,self-care ability and the quality of life of patients with localized small cell lung cancer.