Abstract： Objective To observe the degree of choriocapillary ectasia (CCE) and sub-foveal choroidal thickness (SFCT) in central serous chorioretinopathy (CSC) with different activity and discuss their relations.Methods Forty eyes of 40 CSC patients were recruited.The activity of CSC was determinate by fundus fluorescein angiography (FFA).There were 23 eyes with active CSC (active-CSC group),and 17 eyes with inactive CSC (inactive-CSC group).All eyes in both groups were examined with optical coherence tomography angiography(OCTA),and the CCE area of the choriocapillary layer was measured within a 3 mm× 3 mm zone centered on the central fovea of macula.Ectasia was classified based on CCE area,more than 66％ of examination area was high ectasia,and 33％-66％ as medium ectasia,below 33％ as low ectasia.SFCT was measured with frequency domain optical coherence tomography.The relationship between CCE degree,SFCT and CSC group was analyzed.Results Among the 23 eyes of active-CSC group,there were 5 eyes of low ectasia,12 eyes of medium ectasia,6 eyes of high ectasia.Among 17 eyes of inactive-CSC group,there were 11,4,2 eyes of low,medium and high ectasia respectively.Active-CSC group had more advanced degree of ectasia than that in inactive-CSC group(Z=-2.472,P=0.013).SFCT of active-CSC group and inactive-CSC group were (418.13±-126.15),(429.76±105.80) μm respectively,the difference was not significant (t=-0.308,P=0.760).SFCT in eyes with low ectasia,medium ectasia,high ectasia were (419.13±105.60),(381.00±125.12),(515.13±67.68) μm respectively.The difference among the three group was statistical significant (F=4.106,P=0.025).SFCT in eyes of high ectasia was obviously thicker than low ectasia and medium ectasia,the difference was statistical significant (P=0.007,0.048);the SFCT difference between low ectasia and medium ectasia did not appear statistical significance (P=0.326).There was no linear relation between SFCT and CCE degree (r=0.247,P =0.124).Conclusions Active-CSC eyes has more advanced CCE degree than inactive-CSC eyes,but SFCT is the same between the two groups.High ectasia eyes have thicker SFCT.