The present invention provides a thermally-conductive organic additive which (i) is an organic polymer, unlike a thermally-conductive inorganic filler such as ceramic, metal and a carbon material, (ii) is capable of imparting thermal conductivity to plastic by being added thereto, (iii) can reduce the weight of a composition even when added to a resin in a large amount, without causing abrasion on molds and deteriorating an electrical insulation property of the composition, and (iv) provides the composition with excellent molding processability. The present thermally-conductive organic additive includes a liquid crystalline thermoplastic resin which has a mainly-chain structure, wherein a main chain of the liquid crystalline thermoplastic resin contains mainly a repeating unit represented by the general formula (1):

        -M-Sp-     (1)

wherein M represents a mesogenic group; and Sp represents a spacer,
the liquid crystalline thermoplastic resin itself having thermal conductivity of not less than 0.45 W/(m·K).