The growth characteristics of 20-year-old Eucalyptus camaldulensis Dehuh and Leucaena leucocephala (Lam.) Dewit in the monocultures and their mixedspecies plantations in the Yuanmou Dryhot Valley of southwestern China were investigated by a stem analysis. The results showed that all the DBH, height and volume of timber of E. camaldulensis in the mixedspecies plantations grew faster than those in monoculture. The average increment and current annual increment of height of both the species declined. DBH of the two species declined during 5-10 years but increased during 10-15 years beside E. camaldulensis in the mixedspecies plantations, and then all decreased. The changing rates of Logistic growth curve could scale 5-10, 10-25,and25 years as the early growth period, rapid growth period and stationary growth stage, respectively. Based on this model, E. camaldulensis in the monoculture and mixedspecies plantations will obtain the quantitative maturity at the 23 years and 25 years after the trees were planted, respectively, and both the 24 years for L. leucocephala in the monoculture and mixedspecies plantations. Some management measures such as thinning and increasing water and fertilizer supply in the early and rapid growth period were recommended based on this study.