In this study, in PD patients, we assessed mental fatigue by FS-14, detected the levels of 5-HT, iron and related proteins, including transferrin, lactoferrin and ferritin in CSF and serum, and analyzed the correlations among mental fatigue score and the levels of above factors, and attempted to figure out the mechanisms underlying mental fatigue relating 5-HT and iron metabolism in PD patients with fatigue. Here, LTF is linked to Parkinson disease.