Alloying effects on the electronic structures were investigated for both b. c. c. Zr and h. c. p. Zr in order to obtain useful information for alloy design. The electronic structure was calculated using the DV-Xα cluster method, and two alloying parameters, the bond order Bo and the d-orbital energy level Md, were obtained for a variety of alloying elements M in Zr alloys. The binary phase diagrams of Zr-M system and crystallographic structure of Zr-M compound were found to be classfied according to the location in the Bo-Md map. Also it was shown that the activation energy for atomic diffusion could be associated with the bond order.