There is provided a catheter assembly (1) including: a hollow catheter (2) a catheter hub (3), fixed onto a base end portion of the catheter (2), internally having a passage (31) communicating with the inside of the catheter (2) a needle (4) inserted into the catheter (2) a needle hub (5), fixed onto a base end portion of the needle (4), capable of being connected to a base end side of the catheter hub (3) a valve element (7), positioned to block the passage (31), having an opening and closing unit (71) capable of being opened and closed an operation member (8) having a tubular body, provided such that one opening portion (85) thereof is inserted into the opening and closing unit (71) to cause the base end side and a tip side of the catheter hub (3) to communicate with each other and a communication unit (9), provided on an inner periphery portion of the catheter hub (3) provided with the valve element (7), causing the base end side and the tip side to communicate with each other. In the catheter assembly (1), a sealing member (10) has a tubular body, and is provided between the valve element (7) and the operation member (8) so as to block the communication unit (9) allowing the passage of air yet prohibiting the passage of liquid.
