A method for producing a microbial oil includes genetically modifying a labyrinthulid which belongs to the genus Parietichytrium or the genus Schizochytrium by disrupting and/or silencing a 4 desaturase gene, a C20 elongase gene, and/or a C18 elongase gene, or by being transformed with an 3 desaturase gene; culturing the labyrinthulid; and collecting the microbial oil from the labyrinthulid. The labyrinthulid has an activity of synthesizing DHA via a PUFA-PKS pathway in an amount of not more than 1/100 of a total amount of DHA synthesized in the labyrinthulid or no activity of producing PUFAs via the PUFA-PKS pathway, and the labyrinthulid has an activity of producing PUFAs via an endogenous elongase-desaturase pathway.