To analyze the changes and clinical significance of peripheral blood monocytes and their subpopulations in various phases of Guillain-Barré syndrome (GBS). Methods: One hundred eighteen first onset GBS patients were recruited who were treated regularly and followed up for 18 months. Based on the recurrence of GBS and the readmission to the hospital during the follow-up period, patients were eventually divided into acute-onset GBS (a-GBS) group (n=118), GBS in remission (rem-GBS) group (n=36) and recurrent GBS (rec-GBS) group (n=6). Ninety-six healthy volunteers were included in the control group. Hughes Functional Grading Scale (HFGS) and Medical Research Council (MRC) were performed at each admission. Peripheral blood was collected for routine blood examination and flow cytometry analysis. The changes of peripheral blood monocyte subpopulations and their correlation with MRC summation score were analyzed. Results: Monocytes counts in a-GBS group and rem-GBS group were higher than those in control group (P< 0.05). Classical monocyte (c-Mo) in a-GBS group and rem-GBS group were higher than those in control group and rec-GBS group (P<0.05). Non-classical monocyte (n-Mo) in control group and rec-GBS group were higher than those in a-GBS group and rem-GBS group (P<0.05). The counts of c-Mo were negatively correlated to the MRC sum score in a-GBS group (P<0.05). Conclusion: There were certain variation patterns of peripheral blood monocytes and their sub-populations in various phased of GBS. The increase of c-Mo was positively correlated with the severity of GBS.