A highly unsaturated fatty acid or a highly unsaturated fatty acid ethyl ester that has been produced using as a feedstock oil a fat or oil that contains highly unsaturated fatty acids as constituent fatty acids and which has been reduced in the contents of environmental pollutants, wherein among the dioxins contained, polychlorinated dibenzoparadioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are contained in amounts of less than 0.05 pg-TEQ/g and coplanar PCBs (Co-PCBs) in amounts of less than 0.03 pg-TEQ/g. Also disclosed is a method for producing the highly unsaturated fatty acid or highly unsaturated fatty acid ethyl ester by the steps of removing free fatty acids and environmental pollutants by thin-film distillation from a feedstock oil, ethyl esterifying the resulting fat or oil, and refining the same by rectification and column chromatography.