Abstract： Objective To assess the perfusion changes in brains of patients with varying levels of generalized anxiety disorder (GAD).Methods A total of 38 GAD outpatients of Department of Psychiatry at our hospital from February to August,2014 and 10 healthy controls received a 99mTc-ECD SPECT/CT scan with scenium analysis.Differences between brain perfusion and anxiety levels were analyzed by SPSS 16.0 with one-way ANOVA,Pearson's Chi-square,t test and Spearman's correlation.Results They were grouped according to the levels of anxiety severity,i.e.mild (n =11),moderate (n =16) and severe (n =11).They had significantly lower blood flow in right superior frontal medial gyrus,right precuneus,right putamen,bilateral paracentral lobule and bilateral supplementary motor area (t =-2.19,-2.14,-2.22,-2.34,-2.08,-3.26,-2.72,P ＜ 0.05).Individuals had significantly greater blood flow in mild group than those of control group in right olfactory (t =2.09,P =0.05).Individuals of moderate group had significantly lower blood flow than those of control group in left superior frontal gyrus medial orbital,right superior frontal gyrus medial orbital and left supplementary motor area,but greater in right olfactory (t =-2.16,-2.24,-2.49,2.17,P =0.04,0.04,0.02,0.04).Individuals had lower blood flow in severe group than those of control group in left frontal lobe,right putamen,left paracentral lobule,right paracentral lobule,left precuneus,right precuneus,left parietal lobe,left precentral,right precentral,right postcentral,left rolandic operculum,left supplementary motor area,right supplementary motor area and left central region (t=-2.32,-2.11,-3.16,-2.61,-2.39,-2.18,-2.32,-2.67,-2.14,-2.11,-2.25,-4.38,-3.54,-2.38,P=0.03,0.05,0.01,0.02,0.03,0.04,0.03,0.02,0.05,0.05,0.04,0.00,0.00,0.03).Statistical differences existed in right middle frontal gyrus orbital part (mild:0.96 ± 0.07,moderate:1.03 ± 0.06,severe:0.98 ± 0.08,P =0.04) and left paracentral (mild:0.91 ±0.07,moderate:0.93 ±0.04,severe:0.87 ±0.07,P =0.02).There was a tendency of negative correlation between perfusion in right middle cingulate and paracingulate gyri,left precuneus,right precuneus and left thalamus and anxiety scores by Spearman's correlation analysis (r =-0.28,-0.28,-0.27,-0.29,P =0.09,0.09,0.10,0.07).Conclusion Scenium software provides quantitative measurements for diagnosis of GAD in different anxiety levels.Also larger samples are required for confirming the results in further studies.