The correlation coefficient between the destructives parameter-Modulus of Rupture (MOR) and the non-destruvtive parameters -Modulus of Elasticity (MOE) and Specific Gravity (SG) was verified for three tropical hardwood species - Parkia sp. (Pinho Culabano , Paricã), Vochysia sp. (Cambara, Quaruba), and Hymenaeja sp. (Jatobá), cubing the linear regression technique. The primary objective of this study was the development of an equation of the strength (MOR) related to the non-destructive parameters (MOE, SG) .Such an equation of stress grades ion the classification of structural timbers. The mathematical equation with the best correlation coefficient was one which combined the independent variables - MOE and SG. Nevertheless, for a pratical purpose, the chosen equation as an strength estimate model was MOR = 0,0061 Mb (P) - 11,43816, with a correlationcoefficient of 0,79. Mb (P) Is the Modulus of Elasticity for different loads perspecles applied on the central part of the widest face of the beam. For each species, stress grades were developed according to the average and standard deviation values of the Modulus of Elasticity of the defect-free samples.