Background Patients with major depressive disorder(MDD)may have an abnormal peripheral body temperature rhythm,but its relationship with suicidal risk and the response to treatment with antidepressants remain unknown.Aims This study aimed to investigate the feature of peripheral body temperature in patients with MDD and its relationship with suicide risk before and after treatment with antidepressants.Methods This is a prospective case-control study.Patients diagnosed as MDD were enrolled into MDD group.Healthy subjects who matched in terms of gender,age and body mass index were enrolled into normal control(NC)group.The 24-hour peripheral body temperatures were monitored by TM'Holter the next day after assessment.Patients with MDD were re-assessed after a 2-week treatment with antidepressants.All temperature data were fitted into cosine curves by Python.Result There were 41 patients with MDD,and 21 NC participants enrolled and completed the baseline assessments before the treatment.Patients with MDD were further divided into subgroup of with suicide risk or without suicide risk.In patients with MDD,the mesor of peripheral body temperature rhythm was higher in both patients with(36.17(0.30))and without suicide risk(36.22(0.27))than the mesor in NC participants before treatment(35.84(0.38),Z=11.82,p=0.003,Kruskal-Wallis test).The phase-delay of temperature before treatment was greater in patients with MDD with suicidal risk(4.71(1.68))in comparison with those without suicidal risk(3.05(2.19))and NC participants(3.19(1.82),Z=9.68,p=0.008,Kruskal-Wallis test).Moreover,phase-delay of temperature was associated with suicide risk in patients with MDD before treatment(OR=1.046,95％CI:1.009 to 1.085,p=0.015,unadjusted;OR=1.080,95％CI:1.020 to 1.144,p=0.009,adjusted by age and sex).Conclusion Patients with MDD might have abnormal peripheral body temperature.The abnormal phase-delay of peripheral body temperature may indicate suicide risk in patients with MDD,depending on validation in large-scale cohorts.