Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Constipation is a prodromal symptom of PD. It is important to investigate the pathogenesis of constipation symptoms in PD. Rotenone has been successfully used to establish PD animal models. However, the specific mechanism of rotenone-induced constipation symptoms is not well understood. In this work, we found that constipation symptoms appeared earlier than motor impairment in mice gavaged with a low dose of rotenone (30 mg/kg·BW). Rotenone not only caused loss of dopaminergic neurons and accumulation of α-synuclein, but also significantly reduced serum 5-HT levels and