The aim of this study is to investigate whether stress softening in the passive oesophagus is reversible after KCl activation. Eight normal male Wistar rats’ oesophagus segments were used in this study. Three series of upload-download cyclic loadings were carried out on each segment; each series contained 15 cyclic loadings with 3 pressure levels. The first and second series were done in passive Krebs solution (Ca
-free and EGTA-containing) with an interval of 10 minutes between the two series. After that, each segment was incubated in active Krebs solution (Ca
-containing) for 1 hour and contracted with KCL (110mmol) for 3 minutes. Subsequently, the KCl was washed out, and then carried out the third series of cyclic loadings in passive Krebs solution. The stress-strain curves were used to analyze the time-dependency (viscoelasticity) and the stress softening. The peak stress and stiffness produced during the first loading were bigger than those produced in the remaining loadings. The loop area during the first cycle was larger than in subsequent cycles, indicating the loss of the energy stored in passive structure element after the first cycle. The energy loss due to the viscoelasticity was reversible whereas the energy loss due to stress softening was irreversible in the passive state. However, after 3min activation with KCl, the energy lost due to stress softening was recovered. In conclusion, the stress softening in the circumferential direction in rat’s oesophagus can be reversed by activation with KCl.