A utility knife is provided, including: a first housing, a second housing, a blade carrier and a locking mechanism. The first housing includes a shaft disposed thereon and having an axis. The second housing is rotatably mounted to the shaft and includes a first engaging portion. The blade carrier is movably received between the first housing and the second housing, and is operable to move. The locking mechanism is disposed through the second housing and non-rotatable relative to the shaft. The locking mechanism is axially slidable between a locking position and a releasing position along the shaft and rotatable about the axis. When the locking mechanism is in the locking position, the second housing is non-rotatable relative to the first housing; when the locking mechanism is in the releasing position, the second housing is rotatable about the locking mechanism and rotatable relative to the first housing.