Using five stand ages of Eucalyptus plantations in Guangxi province (young stand (1 a), half-mature stand (2 a), nearly mature stand (3 a), mature stand (5 a) and over mature stand (8 a)), the C, N, and P contents in the leaves, branches, stems and roots in the plantations and their allocation patterns of ecological stoichiometry characteristics were analyzed, respectively. Meanwhile, the dynamics of allocation pattern and stoichiometry characteristics with stand ages, the relationship among them, and their responses to the environment were also investigated. The results showed that there were no significant differences among the organic carbon content in different organs. And, the organic carbon content was no significantly changed with the stand ages. The content of N and P in leaves was relatively high, the ratio of N to P of each organ decreased first and then increased with the increase of stand ages. Compared with other organs, Eucalyptus leaves had characteristics of higher ratios of C to P, and lower N to P and C to N ratio. The N to P ratio of eucalyptus leaves, in half-mature stand, near mature stand and mature stand, were all less than 14, indicating that the growth processes of eucalyptus in these three stands were limited by N.