Abstract: The main objective of this study was to establish a non destructive method for estimating the aboveground biomass of a plant species in the Tunisian arid area. We attempted to establish some models that could be used to predict the species biomass production. Field experiments were carried out on a Poaceae of a high range value Cenchrus ciliaris. The allometric relationships between the plant volume and aerial biomass were studied in autumn 2005 and spring 2006 seasons in southern Tunisia. Linear and nonlinear regressions were tested to establish the best correlations between individual aboveground biomass and plant volume parameters. Measured parameters were the plant height (H) and canopy diameters. Firstly, a model of volume (canopy elliptical cylinder) was tested as a predictor of plant biomass using nonlinear regression. Secondly, It was tested various relationships between the plant biomass and the mean canopy diameter (as the average of the longest canopy diameters maintained perpendicular to each other). Correlations between the aerial biomass production of individuals and their volumes produced a relatively high coefficient of determination (R2 = 0.68). Also, correlations between the mean canopy diameter and the biomass production of individuals produced the best significant relationships with the highest R2. The use of the mean canopy diameter seems to be more practical for the plant biomass prediction.