PROBLEM TO BE SOLVED: To provide a lubricity improver for a diesel fuel oil, which sufficiently improves lubricity of the diesel fuel and miniaturizes saturated fatty acid crystals generated when stored during winter in a cooling state.SOLUTION: A lubricity improver for a diesel fuel oil comprises: 1 to 10 mass% of component (A); 0.4 to 4.0 mass% of component (B); and 86 to 98.6 mass% of component (C), where a mass ratio of component (A) to component (B), [(A)/(B)], is 90/10 to 50/50. Here, (A) is a linear saturated fatty acid having 16 to 20 carbon atoms; (B) is a linear unsaturated fatty acid having 18 carbon atoms, which has 1 to 3 unsaturated bonds where all of the unsaturated bonds are trans-type; and (C) is a linear unsaturated fatty acid having 18 carbon atoms, which has 1 to 3 unsaturated bonds where at least one unsaturated bond is cis-type.
