A new acetylenic acid, (10E,14Z)-9-oxooctadeca-10,14-dien-12-ynoic acid (1), was isolated from the edible mushroom Chanterelle (Cantharellus cibarius), together with a known acetylenic acid, (10E,14Z)-9-hydroxyoctadeca-10,14-dien-12-ynoic acid (2) and their structures were determined through analysis of NMR and mass data. The new acetylenic acid (1) specifically activated peroxisome proliferator-activated receptor (PPAR)-γ with an EC(50) value of 1.88 μM as measured by a reporter gene assay. Expression of PPAR-γ target genes were significantly altered as well, supporting the hypothesis that compound 1 is a PPAR-γ potential agonist that regulates transcription of the PPAR-γ target genes.