The present invention provides an embolus forming in-vivo indwelling coil with high flexibility which can be securely indwelled at a predetermined position and which permits a secured re-indwelling operation and thus has high safety and high operationality.An embolus forming in-vivo indwelling coil of the present invention includes a coil main body having flexibility and an stretch suppressing member which is provided on one or both of the inner and outer peripheries of the coil main body and which is made of a water-swellable polymer material for suppressing stretch of the coil main body by swelling with absorbed water. In the embolus forming in-vivo indwelling coil of the present invention, the water-swellable polymer material constituting the stretch suppressing member is preferably composed of a polyvinyl alcohol polymer.
