AIM To investigate the efficacy of combined use of sodium oligomannate on psychological and behavioral symptoms in patients with mild to moderate Alzheimer’s disease (AD). METHODS Mild to moderate AD patients with behavioral and psychological symptoms of dementia (BPSD) who visited the outpatient department and inpatient department of our hospital from January 2021 to June 2022 were randomly divided into two groups. The control group was orally administered with donepezil at an initial dose of 5 mg·d^-1, which increased to 10 mg·d^-1 after 4 weeks. On the basis of taking donepezil, the study group combined the use of sodium oligomannate, 450 mg each time, twice a day. The two groups were all treated for 8 weeks. The mini-mental state examination (MMSE) and neuropsychiatric inventory (NPI) were assessed and compared between the two groups at baseline and after 4 and 8 weeks of treatment. The general linear model was used to analyze the effect of combined use of sodium oligomannate on the improvement of NPI scores after the 8-week treatment. RESULTS Finally, 60 patients completed the clinical study, with 30 in each group. The total score of NPI in two groups was significantly decreased compared with baseline after 4 weeks and 8 weeks of treatment (P<0.05), and the decrease was more significant in the study group with significant difference between groups (P<0.05). Compared with the baseline, the scores of apathy, depression, anxiety, and irritability in the study group were significantly decreased at the end of 4 weeks (P<0.05), and agitation and delusion scores were also significantly decreased at the end of 8 weeks (P<0.05). Compared with the control group, the study group showed a more significant decrease in depression, anxiety, agitation, irritability, and appetite scores compared to baseline after 4 weeks of treatment (P<0.05), and a more significant decrease in emotional apathy score after 8 weeks of treatment (P<0.05). The MMSE scores of the two groups were significantly higher than those of the baseline at the end of 4 and 8 weeks (P<0.05). There was no significant difference in the incidence of adverse reactions between the two groups (P>0.05). CONCLUSION Combined use of sodium oligomannate can not only improve the cognitive function of AD patients, but also improve their BPSD, especially emotional problems such as anxiety, depression, agitation, and irritability, without obvious adverse reactions.