Provided is a catheter assembly (1) equipped with: a hollow catheter (2) a catheter hub (3), fixed onto the base end of the catheter (2), internally having a passage (31) communicating to the inside of the catheter (2) a needle (4) which is inserted into the catheter (2) and a needle hub (5), fixed onto the base end of the needle (4), capable of being connected with the base end side of the catheter hub (3). This catheter assembly (1) has: a valve element (7), having an opening and closing unit (71) capable of opening and closing, positioned to choke the passage (31) an operating member (8) having a tubular body, arranged so that one opening (85) is inserted into the opening and closing unit (71) to communicate the base end and the tip of the catheter hub (3) and a communicating unit (9), arranged on the inner perimeter of the catheter hub (3) equipped with the valve element (7), which communicates the base end and the tip. In this catheter assembly (1), a sealing member (10) having a tubular body, which allows the passage of air yet blocks the passage of liquids, is arranged between the valve element (7) and the operating member (8), as to close the communication unit (9).
