Radial wood variation patterns were determined for quebracho blanco (Aspidosperma quebracho-blanco L.) one of the most important species of The Chaco Region. Ten adult trees from two sites, trees per site were used. From each tree, disks were removed at breast height. Patterns of variation of pore area, fibber diameter, lumen fibber, fibber cell wall thickness, percentage of pores, fibbers, parenchyma and rays were examined using sites, trees and radial distances as sources of variation. Univariate analysis was performed using a nested design, with random effect on sites and trees and fixed on distance to the pith. Variance Components were estimated by Restricted Maximum Likelihood. The results showed that distance to the pith was the main source of variation for the traits studied. The wood anatomical features studied were not affected by site. Fibber diameter, fibber cell wall thickness and pore percentage showed an increasing pattern along the radius. The diameter lumen fibber, fibbers percentage and rays percentage showed a not definite pattern of radial change. Along the radius the tissue proportions of fibber diameter, and fibber cell wall thickness increased more rapidly up to a distance of 10,5 cm. Mature wood was not observed up to the distances studied.