PURPOSE: To obtain a waterproof optical cable having sufficiently good connecting characteristic and resistance to permeation of water by filling a moisture preventing mixture in the grooves and a water-absorptive swellable material in the spaces between elements constituting the cable other than the grooves.

CONSTITUTION: Six of a hundred core optical fiber unit housing four sheets of five core tape-shaped optical fiber core wires 1 layer-built in each spiral groove of PE spacer 2 provided with five lines of spiral grooves on the external periphery of a core body having 9.0mm outside diameter, are twisted together around the external periphery of an aggregate of high-tensile bodies 3, to constitute the optical cable. The sectional dimension of the spiral groove is 2.0mm breadth × 2.2mm depth, and the pitch of the spiral is 500mm. The outside diameter of the cable is 36mm, and the weight is 1.0kg/m. The moisture preventing mixture to be filled in the spiral groove is silicone gel, and the water-absorptive swellable material to be filled in other spaces is crosslinked carboxymethyl cellulose. By this constitution, a waterproof optical cable having superior transmitting characteristic, mechanical characteristic, and waterproof characteristic is obtd.