The Dual energy method, using two different energies generated by an X-ray tube, has been applied in the diagnosis of osteoporosis by determining bone mass or bone density. By measuring parameters that characterize bone quality, such as the Ca/P or Hydroxyapatite/Collagen (HAp/Col) ratios, a potential bone fracture can be predicted more efficiently. The aim of this study was the optimization of dual energy X-ray spectra through the estimation of the Coefficient of Variation (CV) in HAp/Col ratio determination. The upper limit of CVHAp/Col value was set to ≤ 3%. Single and double exposure methods were used in order to obtain polyenergetic spectra. Unfiltered spectra were obtained from Boone et al (1997 Med. Phys. 24 1661–70) for Tungsten (W) anode. For the implementation of the low and high energy beams, several filters were applied to the spectra, based on their K-edges, so as to provide quasi-monochromatic beams. The optimum results, for the single exposure method, were obtained for a 120kVp spectrum with added beam filtration of 800um Ce (CVHAp/Col=1.88%). For the double exposure technique, a CVHAp/Col value of 2.23% was obtained using 40 and 120kVp with added filtration of 250um Cd and 1150um Yb, respectively.