An introducer assembly formed by previously integrating an introducer sheath and a dilator together. The introducer assembly is configured so that the blood stop performance of a blood stop valve can be maintained for a long period of time and so that the essential function of a dilator tube is not impaired. An introducer assembly is configured in such a manner that a dilator tube (50) is inserted through the insertion section (41) of a blood stop valve (40) and that an introducer sheath (11) and a dilator (13) are previously integrated together. When a cap (12) is pressed toward the base end surface of a sheath hub (30) and engaged with the sheath hub a deformation member (90) disposed between the blood stop valve and the cap (12) presses the blood stop valve to apply a compression force which acts in the direction in which the insertion section is set in a closed state.
