Abstract: A catheter for guiding a body fluid of a subject includes an elongated body, an adjusting mechanism, and a valve mechanism. Moreover, the elongated body further includes a first portion, a second portion and a flexible portion between the first and the second portions. The second portion includes a passageway for the body liquid. The valve mechanism closes to the inlet of the passageway. Furthermore, the flexible portion expands when the adjusting mechanism is in a first state to prevent the catheter from being removed from the subject, and the flexible portion retracts when the adjusting mechanism alters to a second state to allow the catheter to be removed from or inserted into the subject. Hence, the body fluid is directed to enter the passageway via the inlet and exit via the outlet when the adjusting mechanism is not in the second state.