Abstract: Soil fertility analyses in a mixed bamboo forest and two pure bamboo forests transformed at different growth stages from mixed stands at various times had been done and the results showed the natural soil fertility in a mixed bamboo stand was better than those in pure bamboo stands in the neighbouring sites after a longterm management.As the management term of pure bamboo stands prolonged the natural soil fertility declined,which resulted from the growth characteristics of pure bamboo forest and the management methods. The soil fertility in pure bamboo stands declined faster in the first 10 years than that in the second 10 years after they were transformed from mixed forest with trees.The fertility index varied at different rate during the period. The rhizomes and root of bamboo affect the soil porosity obviously.