Finite element (FE) method is extensively employed to investigate the biomechanical behavior of bone structures. Material and morphological information of bone samples are typically provided by computed tomography (CT) scanning. Assuming that density and elasticity of bone are correlated, many studies have proposed different density-elasticity relationships to determine bone elastic constants. Herein, an innovative method for determining a single mathematical relationship between bone density and elasticity is proposed. Density distribution and morphology of a bovine bone were obtained from CT images, and the natural frequencies were measured using experimental modal analysis. The relationship between density and elasticity has a standard mathematical form with variable constants. Genetic algorithm (GA) was used to obtain the constants by minimizing the discrepancy between experimental and FE results. The relationship was then used in material properties assignment process of FE modeling and proved to be valid by predicting the natural frequencies of bone in different boundary conditions (BCs).