Objective To study in vitro degradation behavior of absorbable suture made of poly(pdioxanone) (PPDO) with high molecular weight (Mv=4× 105～5 × 105) in simulated internal environments of the digestive tract with different pH values.Methods Absorbable suture samples were immersed in 3 kinds of phosphate buffer solution(PBS) with pH values of 1.2,7.4 and 8.5 which were put into a shaker at constant 37 ℃C.Samples were retrieved at 2,4,6,8,10,12 weeks after immersion for gross observation of their morphology and color change followed by measurement of their wet and dry weight,scanning electron microscopy,infrared scanning and mechanical tests.Results Great mass loss and water absorption change were observed during the in vitro degradation of PPDO.At 4 weeks,the mass loss rate and water absorption rate were respectively 55.91％ and 6.89％ in pH=1.2 group,1.28％ and 2.44％ in pH=7.4 group and 2.03％ and 3.93％ in pH=8.5 group.The initial PPDO had a high tensile strength (112.36 MPa) and a high elongation at break (74.83％).PPDO lost its mechanical properties in strong acid environments as the degradation progressed.At 4 weeks,the tensile strength of pH=7.4 group reduced to 61.97％ and the elongation at break to 37.53％ ； the tensile strength of pH=8.5 group reduced to 53.73％ and the elongation at break to 35.16％.At 4 weeks,its mechanical strength changed significantly,but still ＞50％,but at 6 weeks its mechanical strength decreased sharply and radical external changes were observed.Fourier transform infrared scanning showed no new bond groups during degradation.Conclusions The high molecular weight PPDO degrades slowly and has good stability in neutral and alkaline conditions but faster in acidic conditions,indicating hydrolysis is its degradation mechanism.Therefore,in cases of severe reflux esophagitis,PPDO esophageal stents may need an additional anti-reflux device to reduce the degradation by acidic substances and alleviate symptoms of the patients.