An unusual fatty acid, cis-9,cis-15-octadecadienoic acid, has been identified in the pulp lipids of mango (Mangifera indica L.) grown in the Philippines. To our knowledge, the occurrence of cis-9,cis-15-octadecadienoic acid in higher plant lipids has not been previously reported. The structure confirmation was based on the results of chromatographic (capillary GC, argentation thin-layer) and spectrometric (GC-MS, infrared, ultraviolet) analysis and chemical treatment. This butylene-interrupted dienoic fatty acid is concentrated in the pulp part of mango fruit and occupies 5.4% of total acyl groups in the pulp lipids; whereas a common octadecadienoic acid, linoleic acid, is a minor component (1.1%) in the same lipids. If a trivial name is desired, it is suggested that cis-9,cis-15-octadecadienoic acid be called "mangiferic" acid.