Disclosed herein is a catalytic converter anti-theft device for motor vehicles. The anti-theft device a motor vehicle catalytic converter anti-theft device comprises a first shell component configured to surround, at least in part, a first portion of a motor vehicle catalytic converter. A second shell component is configured to surround, at least in part, a second portion of the motor vehicle catalytic converter. The first shell component and the second shell component are configured to be attachable to each other in coaxial relation about the first portion of the catalytic converter and the second portion of the catalytic converter, respectively. A distal end of at least the first shell component comprises a structure configured to prevent axial movement of the first shell component relative to the catalytic converter. At least the first shell component further may be attachable to a fixed component of the motor vehicle.