Objective To study the influence of madopar for 5-HT in platelet and depressive symptoms of Parkinson's disease patients.Methods We observed 5-HT in platelet of 35 PD cases in our hospital who take madopar at least one year.At the same time, we observed the mental symptoms change of every case before and after the treatment.Results Madopar can significantly lower the 5-HT of platelet after one year, and HAMD score results show that madopar is significantly higher before treatment.Conclusion Madopar can damage serotonin neurons in the brain, which may enhance the patients with depressive symptoms.