The objective of this study was to evaluate whether there is the influence of different clonal hybrids of Eucalyptus urophylla on the carbon concentration and amount in below-ground biomass in trees cultivated in Oxisol, Brazil. Stumps and roots of three different eucalypt hybrid clones, AEC 0144, AEC 0223, and VM01, were selected, weighed immediately after removing from the ground, and sampled for carbon determination and moisture content at the laboratory. The Shapiro-Wilk’s and Bartlett tests were used to evaluate data distribution and the homogeneity of variances, respectively. Analysis of variance (ANOVA) complemented by the Scott-Knott test was used to evaluate the effects of specie/hybrid on the below-ground biomass (dry matter) and carbon amount per stump. The hybrid type of Eucalyptus urophylla does not influence the carbon concentration; however, there is a difference in below-ground biomass production and carbon amount being higher for Eucalyptus urophylla x Eucalyptus camaldulensis when compared to the species Eucalyptus urophylla and hybrid Eucalyptus urophylla x Eucalyptus grandis.