Abstract: The components of the fatty acid and the contents of octadecatrienoic acid in radish seed were analyzed. The radish seed oil was extracted by soxhlet extraction. The obtained fatty oil was esterified by sodium hydroxide-methanol. The fatty acid was separated and identified by gas chromatography-mass spectrometry（GC/MS）. Nine fatty acids are identified in the radish seed, the main components are unsaturated fatty acids. The unsaturated fatty acids are octadecatrienoic acid, octadecadienoic acid and 13-docosenoic acid， respectively. The content of octadecatrienoic acid， in radish seed was determinated by high performance liquid chromatography(HPLC).