A catheter assembly includes: an inner needle； an inner needle hub connected to the inner needle； a catheter through which the inner needle is inserted； a catheter hub connected to a proximal end portion of the catheter； and a protector that covers at least the tip of the inner needle when the inner needle is withdrawn. The protector includes: an inner tube, and an outer tube. The inner tube includes at least one arm that releasably engages with a proximal end of the catheter hub. The catheter assembly is configured such that, when the inner needle is withdrawn, after the tip of the inner needle has been stored in the protector, the outer tube is retracted with respect to the inner tube thereby allowing the at least one arm to be displaced outwardly, whereby engagement between the at least one arm and the catheter hub is released.
