To obtain a lubricity improving additive capable of improving lubricity of a middle distillate at a low addition rate, and uniform, transparent, and especially having fluidity even at a low temperature.

This invention is related to an additive having low temperature stability and used for a fuel oil having a sulfur content of not higher than 0.05 wt.% comprising a mixture of following fatty acids and the use of the mixture for improving lubricity performance of a low sulfur middle distillate. The mixture comprises 1-99 wt.% at least one kind 6-50C saturated mono or dicarboxylic acid (A1), 1-99 wt.% at least one kind 6-50C unsaturated mono or dicarboxylic acid (A2), and at least one kind polar nitrogen containing compound (B) as a paraffin dispersant effective in the middle distillate at 0.01-90 wt.% based on the total weight of (A1), (A2), and (B).