A catheter assembly includes an inner needle a catheter through which the inner needle extends and a catheter hub retaining the catheter a needle cover that accommodates the inner needle when the inner needle is withdrawn from the catheter, the needle cover including: an inner tube attached to and detached from a catheter hub, the inner tube including a stopper portion, and an outer tube covering a portion of the inner tube, and moving relative to the inner tube when the inner needle is withdrawn. The stopper portion prevents relative movement between the inner tube and the outer tube in a standby position proximate to a radially outer side of the inner tube, while the inner needle extends through the catheter. The stopper portion slides to a blocking position accompanying relative movement of the outer tube with respect to the inner tube when the inner needle is withdrawn.
