Objective To observe the dynamic changes of 18F-FDG uptake and clearance in the amygdala and hippocampus in patients with first-episode depression (FED),and explore the neurobiology mechanism of FED.Methods i8 F-FDG PET/CT imaging was performed on 35 patients with FED and 35 healthy volunteers from January 2014 to January 2016.SUV in the amygdala and hippocampus at different time points were collected.The clearance rates were calculated and the difference between patients and healthy volunteers were compared by two-sample t test.Results The FDG uptake in the left amygdala of patients reached the peak earlier compared with that in the healthy group,with the SUVmax of 12.94±2.03 at 25 min and 10.50±1.79 at 40 min,respectively.FDG uptake in the left amygdala at 10,25,40,55,70,85 min between the 2 groups were significantly different (t values:12.92,8.65,6.99,12.34,28.87,13.87;all P＜ 0.05).The clearance rate in the left amygdala of patients at different time interval was increased compared with that of the healthy group(40-55 min:t=32.53;56-70 min:t=32.73;71-85 min:t=11.10;all P＜ 0.05).Compared with the healthy group,FDG uptake in the left hippocampus of patients was decreased significantly at 10,25,40,55,85 min (t values:2.70,7.75,7.78,8.81,7.00;all P＜0.05) for FDG uptake,and the clearance rate was also decreased significantly at different time interval(40-55 min:t =6.02;56-70 min:t=62.15;71-85 min:t=37.39;all P＜0.05).Differences of metabolic changes in the right amygdala and the right hippocampus were not significant.Conclusions 18F-FDG metabolism in the amygdala and hippocampus of patients with FED may be abnormal,which is characterized by earlier peak uptake and quicker clearance in the left amygdala while lower uptake and slower clearance in the left hippocampus.