Provided is a one-pack type ultraviolet-thickenable thermally conductive silicone grease composition which, at the initial stage, has a low viscosity (is easy to apply) but has high shape retentivity and which, after curing, is pliable (has low hardness). The ultraviolet-thickenable thermally conductive silicone grease composition comprises, as essential components, (A) an organopolysiloxane having a viscosity at 25 DEG C of 50-100,000 mPa*s and containing at least one alkenyl group in the molecule, (B) a liquid organohydrogenpolysiloxane which has a viscosity at 25 DEG C of 100 mPa*s or less, contains 2-10 silicon-atom-bonded hydrogen atoms in the molecule and contains at least one alkoxy and/or epoxy group bonded to a silicon atom through an alkylene group and in which the polysiloxane has a degree of polymerization of 15 or less and the skeleton of the polysiloxane includes a cyclic structure, (C) a photoactivable platinum complex curing catalyst, and (D) a thermally conductive filler having a thermal conductivity of 10 W/m*DEG C or greater.