Abstract: A quantitative analysis of 20-hydroxyecdysone was carried out by HPLC for Cyanotis arachnoidea and 13 other species of Commeliaceae, which were distributed in Yunnan and be- longed to three tribes and ten gerena. The results showed that most species contained 20-hydroxyecdysone in trace, so it did not have any chemotaxonomic importance to Family Commeliaceae. The dynamic variation of 20-hydroxyecdysone in different collecting places and seasons of C.arachnothea was also analysed. It is noticed that the contcnt variation of 20-hydroxycdysone in both overground and underground parts of the annual planting of C. arachnothea are interrelated with that of the visit by butterflies.

Key words: Cyanotis arachnoidea