Alumina thin films are deposited inside the channels of stainless steel tubular reactors by atomic layer deposition (ALD) to deactivate the metal surface for the purpose of coke suppression. The ALD equipment is modified to incorporate the high-aspect-ratio metal tubes into the flow path of the ALP system. Experimental parameters are adjusted to ensure complete and uniform coverage of the internal surfaces of the metal tubes. The thicknesses of the passivation layers are precisely controlled by adjusting the number of ALD cycles. In coking experiments, the passivated metal tubes are used as reactors for thermal cracking of a hydrocarbon fuel composed of C-12-C-16 paraffins. The lifetime of the experimental system passivated by ALD alumina films can be up to 5 times longer than that of the system using bare metal tubes as the reactor. When the tested metal tube samples are analyzed, it is discovered that the ALD,alumina film remains intact after the coking experiment, indicating that the metal-catalyzed filament coke formation can be completely inhibited, by the ALD alumina passivation layer.