Abstract: Oncidium aloha ‘1wan ga’ in vitro shoots were used as plan t materials for experiments to study the efect of difierent sucrose concentrations (30，20，10，5，2．5，0 g·L )in the culture medium on the growth 0f the in vitro sho ts under CO，enrichment conditions． The results showed that the in vitro shoots had photoau totrophic capability． Under CO2 enrichm ent conditions， in vitro shots being cultivated in the sugar-free culturemed ium could grow normally by photoautotrophic capab ility，but a bit slowly． Increas ing the sucrose concentration in the culture medium could significan tly promote the growth of the in vitro shots of Oncidi． Under CO2 enrichment condition． in vitro sho ts grew be tter in the sugar culture medium than in the sugar-free culture medium ．Compared th the sucrose concentration (30 g·L )un der normal culture conditions ，when the sucrose concen tration dropped to 20 g·L|。． there was not significan t difference be tween the tw o concentration treatments in the main growth indices of the in vitro shots including plant height， length of leaves， range of leaves， number of roots． total fresh mas s an d dry matter mass． The above results indicate that under C02 enrichm ent cul ture conditions． the existence of sucrose in the culture medium is still necessary for Oncidium ，but compared with normal culture methods． it can partly reduce the amount of sucrose used in the culture medium ．

Key words: Oncidium, Carbon dioxide, Caseous fertilizer, Sucrose content, In vitro cullure, Medium