Species specific allometric equations are important for accurate net aboveground biomass estimation and quantifying carbon stock in living tree biomass of terrestrial ecosystems. This study was undertaken to develop species-specific allometric equation semi-destructively of two indigenousand one exotic tree species namely Mytenu sobscura, Rosa abyssinica and Eucalyptus globulus respectively in Egdu forest of Oromia Region. Currently, like that most Ethiopian forest such model did not exist for this particular species by this methodology. The data was taken from 12 individuals of each species with different DBH class intervals. Preferential sampling method was used to collected data by DBH class. The allometric equations were developed by relating tree component biomass to DBH or basal diameter. Four equations with high adjusted R2adj&correlation and low AIC & RSE value were selected for each tree species and the statistical analysis was highly significant (p<0.000) fit for linear models for all species and displayed minimal bias. They had a mean total biomass of 118.24 kg, 43.54 kg and 1026.52 kg for Mytenus obscura, Rosa abyssinica and Eucalyptus globules respectively. It is understood that previously published general allometric model reveal errors of over estimation of biomass in higher DBH classes and underestimation in lower DBH classes, and the formulated new equations will be used in the future for the selected three tree species. And it would create an opportunities for sustainable management of forest and to mitigate climatic change through increasing the household income through better assessment of biomass and carbon finance. Key words: Allometric model, Biomass, species specific, Egdu forest, semi-destructive method.