A process for producing a flame-retardant, silane-crosslinked polyolefin, characterized by melt-mixing a flame-retardant polyolefin consisting of an .alpha.-olefin polymer, a flame-retardant, a water-absorbing agent and a silanol-condensing catalyst with a substantially water-free carrier polymer comprising an organic unsaturated silane and a free-radical generator at a higher temperature than the crystalline melting point of the base polymer of the flame-retardant polyolefin to subject them to reaction and then contacting the reaction mixture with water to subject the reaction mixture to crosslinking.