Neutral intermediate boson, Z boson, is expected to be observed at high energy accelerators in the near future. Assuming that Z boson mass is thereby determined, we give prediction for the mass of the charged intermediate boson, W± boson, at 1· loop level of the electroweak interaction. Presently, many particle physicists believe the existence of heavy inter mediate bosons of the weak interaction, that is, W± and Z bosons. Although nobody has obtained direct evidence of their existence, it is highly expected that future accelerators will soon produce them. As for their masses, tree level analyses of various experimental data in the Weinberg-Salam theory!) predict