<P><B>Abstract</B></P><P><B>Aim</B></P><P>To find <I>cis</I>‐11‐eicosenoic acid (20:1<I>ω</I>9, EA)‐producing micro‐organisms.</P><P><B>Methods and Results</B></P><P>We found EA‐producing fungi by screening about 300 fungal strains and identified a major fatty acid accumulated in the <I>Mortierella</I> fungi as EA by means of GC‐MS analysis. In particular, <I>Mortierella chlamydospora </I>CBS 529.75 produced a high amount of EA (36·3?mg?g<SUP>−1</SUP> of dried cells) on cultivation at 28°C for 4?days and then at 12°C for 3?days. In the result of lipid analysis, most of the EA was a component of triacylglycerols, not phospholipids.</P><P><B>Conclusion</B></P><P>We found that <I>M.?chlamydospora </I>CBS 529.75 was the best producer for the microbial production of EA.</P><P><B>Significance and Impact of the Study</B></P><P>EA is beneficial as a raw material for medical supplies and a moisturizing component of cosmetic creams. This is the first report of microbial production of EA.</P>