<jats:title>Abstract</jats:title> <jats:p>A new icosanoid lipobetaine has been isolated from a red alga and its structure has been determined to be (2S)-2-[(3S)-3-[(5Z,8Z,11Z,14Z,17Z)-5,8,11,14,17-icosapentaenoyloxy]-(8Z,11Z,14Z)-8,11,14-icosatnenoylamino]-5-trimethylammoniopentanoate, mainly on the basis of NMR spectral and chemical means.