A titanium or titanium alloy composite having a porous surface layer, which comprises a titanium or titanium alloy substrate and a porous titanium or titanium alloy layer that adheres strongly to said substrate, said porous layer being formed by first providing said substrate with a firmly adhering sinter of a mixture of a titanium or titanium alloy powder and a magnesium powder, and then removing magnesium from the sinter. A process for producing a titanium or titanium alloy composite having a porous surface layer, comprising: providing a coating composition comprising a binder added to a mixture of a titanium or titanium alloy powder and a magnesium powder; applying said composition to the surface of a titanium or titanium alloy substrate; heating the substrate at a temperature of from 650 DEG to 800 DEG C. in vacuo or an inert atmosphere so as to form a sinter of the powders of titanium or titanium alloy and magnesium which firmly adheres to said substrate; and removing magnesium from said sinter.