Objective To explore the clinical value of endoscopic ultrasonography (EUS) examination before esophageal achalasia (EA) patients treated by peroral endoscopic myotomy (POEM).Methods From August 2011 to November 2011,esophageal EUS examination was conducted in 34 EA patients scheduled for POEM treatment (EA group) and 30 cases accepted gastric EUS examination (control group) at endoscopic center,Zhongshan Hospital,Fudan University.The thickness of muscularis propria layer and the circular muscle layer was measured at cardia,5 cm,10 cm and 15 cm above cardia,and the proportion of circular muscle layer was calculated.The differences in groups and between groups were compared.The correlation between muscle thickness and complication after POEM treatment was analyzed.The data were analyzed by t test.Results There was no difference between EA group and control group in the thickness of the muscularis propria layer at same part (at cardia,5 cm,10 cm and 15 cm above cardia,t=1.210,1.116,0 and 0.292respectively; all P＞0.05 respectively).The thickness of the circular muscle layer of EA group at cardia,5 cm,10 cm and 15 cm above cardia was (1.72±0.49) mm,(1.86±0.81) mm,(1.56±0.47) mm and (1.41±0.48) mm respectively,those of control group was (1.06±0.50) mm,(1.40±0.33) mm,(1.05±0.37) mm and (0.78±0.12) mm respectively.At same part,the thickness of the circular muscle layer of EA group was significantly thicker than that of the control group (t =5.326,2.903,4.778 and 6.993 respectively,all P＜0.05).After POEM treatment,complication was high in EA cases with the thickness of muscularis propria layer less than 2 mm.Conclusion Before POEM treatment,EUS examination for EA patients has certain guiding significance.