A crude microbial oil comprises arachidonic acid (20:4 ω6) as highly unsaturated constituent fatty acid, at not less than 30% by weight arachidonic acid content based on total fatty acid in the crude oil. The ester-type sterol content of the fat or oil is not more than 0.8% by weight. Also disclosed is a process for producing such crude oil by culturing a microorganism in a medium containing nitrogen source at a concentration of 2 to 15% in a culture tank equipped with an agitation impeller satisfying the requirement that the ratio of the diameter of the agitation impeller (d) to the inner diameter of the culture tank (D) is d/D = 0.30 to 0.6.
