Crude sample solution prepared from the seeds of Castanosperum australe was fractionated by preparative liquid chromatography. The fractions thus obtained were subsequently analyzed by means of thermospray liquid chromatography-mass spectrometry (tsp lc-ms). Under the conditions employed, castanospermine [1], 6-epi-castanospermine [2], australine [3], 3,8-di-epi-alexine [4], and fagomine [5] could be separated and detected. The possible structures of other castanospermine-related alkaloids found in the crude sample solution are also discussed.