Objective To investigate the clinical effect of Kaixin Powder in the treatment of breast cancer patients with insomnia and its effect on the serum level of 5-hydroxytryptamine (5-HT). Methods A total of 63 breast cancer patients with insomnia were randomly divided into treatment group with 30 patients and control group with 33 patients.The patients in the control group were given oral administration of estazolam, and those in the treatment group were given Kaixin Powder combined with estazolam.The two groups were compared in terms of Pittsburgh sleep quality index (PSQI),Self-rating Depression Scale (SDS),Self-rating Anxiety Scale (SAS), European Organization for Research and Treatment of Cancer-Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30), and serum 5-HT level before and after treatment, and after treatment for 4 consecutive weeks, the two groups were compared in terms of clinical outcome and the incidence rate of adverse reactions.Results After 4 weeks of treatment,both groups had significant reductions in PSQI, SDS, and SAS scores (P<0.05),and the treatment group had a significantly lower PSQI score than the control group (P<0.05);compared with the control group,the treatment group had significantly higher scores of physical function,emotional function,cognitive function,and social function in EORTC QLQ-C30 (P<0.05);after treatment, both groups had a significant increase in the serum level of 5-HT (P<0.05),and the treatment group had a significantly higher serum level of 5-HT than the control group (P<0.05).Compared with the control group, the treatment group had a significantly better clinical outcome(P<0.05) and a significantly lower incidence rate of adverse reactions (P<0.05). Conclusion Compared with estazolam alone for patients with breast cancer, Kaixin Powder combined with estazolam can better alleviate insomnia, increase the serum level of 5-HT,improve quality of life,and reduce the incidence rate of adverse reactions.