Thermally conductive grease composition

A thermally conductive grease composition that is non-curable comprising:

• A. 100 parts by mass of an ethylene-α-olefin copolymer with a kinematic viscosity of 10000 mm2/s or less at 40° C.;
• and
• B. 115 to 580 parts by mass of thermally conductive particles with respect to 100 parts by mass of the component A,
• wherein the thermally conductive particles contain the following:
• B1. 55 to 350 parts by mass of irregularly-shaped alumina with a median particle size of 0.1 to 1 μm, in which a part or all of the alumina is surface treated with an alkoxysilane compound expressed by RaSi(OR′)4-a, where R represents a substituted or unsubstituted organic group having 8 to 12 carbon atoms, R′ represents an alkyl group having 1 to 4 carbon atoms, and a represents 0 or 1, or a partial hydrolysate of the alkoxysilane compound;
• B2. 5 to 60 parts by mass of plate-shaped boron nitride with a median particle size of 0.1 to 10 μm;
• and
• B3. 55 to 170 parts by mass of aggregated boron nitride with a median particle size of 20 to 70 μm, and
• wherein a mass ratio of the component B3 to the component B2 is 2 to 20.