The potential soil biological change due to the establishment of Eucalyptus plantations in volcanic soils has not been reported. The objective of this research was to assess the soil quality of Eucalyptus stands growing on a volcanic ash derived soil, compared with a natural forest (Nat-forest, control) and a Pinus radiata stand, previously established to the Eucalyptus stand. A complete randomised design was established (n=4) within Nat-forest and commercial plantations. Soil samples (10 cm) were taken in autumn, to measure soil microbial biomass (Cbiom) by soil fumigation-extraction, and CO2-C respiration (Cmin) from soil microorganisms by soil incubation. Metabolic quotient (q met) was calculated to compare (p ≤ 0.05) the microbial efficiency of the soil biomass between treatments. As expected, Nat- forest showed the largest Cbiom and Cmin (p ≤ 0.05). However, no differences were found between E. globulus, E. nitens and P. radiata (p ≤ 0.05). The low Cbiom and Cmic in Eucalyptus stands might be attributed to the effect of recalcitrant inputs of C from the previous pine plantation, although the efficiency of the soil microbial population (q met) was not affected (p ≤ 0.05) by the C quality of the plantations. Thus, it seems that Eucalyptus stands are not entirely detrimental to the soil quality of volcanic soils of temperate forest ecosystems.