Frequency upoonversion in Yb3+/Er3+ doped silica fibers pumped by a CW106.4 urn laser has boen demonstrated for the first time. The visible fluorescence spectra of Yb3+/Er3+ doped silica optical fibers were measured. Energy transfer process, excited-state-absorption and two-photon absorption of Er3+ ions were proposed to account for the experimental obser-vatiou of three upconverted fluorescence spectral lines at 467., 546 and 667 nm.