We have investigated the thermal quenching effect on the bismuth active center (BAC) in a Bi/Er co-doped fiber (BEDF). The effects from varying quenching conditions are studied and discussed. We report, for the first time to our knowledge, a significant BAC activation achieved by thermal quenching. We observed that the peak luminescence at ∼1405 nm of the BAC associated with silica (BAC-Si) could be enhanced more than two times by thermal quenching. The experimental results indicate that thermal quenching could be an effective way for BAC activation of bismuth-doped fibers.