Abstract: The effects of enhanced UV-B radiation on biomass and contents of camptothecin and 10-hydroxy-camptothecin in Camptotheca acuminata were investigated in a pots experiment.The results showed that:(1)Comparing to the control group,the fresh weight of C.acuminata seedlings and of the various organs did not change significantly in the first 20 days after treatment.After 40 days,however,the biomass of the whole plant and the various organs was higher than in the untreated plants.Finally,the biomasses per plant in the treatment groups decreased,long UV-B radiation caused dwarf seedlings and bold base stem,and also changed the distribution of dry matter during the growth of the C.acuminata,with more dry matter distributed to the stems and roots and less to the leaf.(2)Enhanced UV-B radiation increased the camptothecin content in leaves and stems,but reduced it in the roots;the content of 10-hydroxy-camptothecin fluctuated,occasionally higher than control,and did not show a sensitive response to enhanced UV-B radiation.(3)The content of alkaloid in all organs had a certain correlation with biomass accumulation:the biomass increased rapidly while the secondary products in units mass plants declined.