PROBLEM TO BE SOLVED: To provide a medical connection tool capable of suppressing clogging of a medicine even when a medicine having low fluidity such as a vascular embolus bead, is circulated, and a catheter assembly comprising the medical connection tool.SOLUTION: A medical connection tool 10 comprises a hollow part 40 formed over a proximal side attachment part 20 and a distal side attachment part 30, and when a first medical appliance (syringe 200) and a second medical appliance (sheath 120) are respectively attached to the proximal side attachment part 20 and the distal side attachment part 30, the first medical appliance and the second medical appliance are communicated each other through the hollow part 40. The hollow part 40 comprises: a proximal side part 50 whose diameter shrinks at a first change ratio toward the distal side； and a distal side part 60 disposed on a distal side of the proximal side part 50, and whose diameter shrinks at a second change ratio being smaller than the first change ratio toward the distal side. A length of the distal side part 60 in an arrangement direction of the proximal side part 50 and the distal side part 60 is longer than a length of the proximal side part 50 in the arrangement direction.SELECTED DRAWING: Figure 1
