This paper presents our recent application of Brillouin-based optical fiber sensors for geotechnical monitoring. We embed an optical fiber into a prestressing steel strand (hereafter ‘strand’) during the manufacturing process, where the epoxy-coated strand is fully integrated with the optical fiber without sacrificing long-life durability. We install the strand to prestressed ground anchors for the stabilization of steep slopes. The experimental results indicate that the sensorembedded strand can detect changes in the loaded force on the anchor and can determine the cause of such changes. As a field application, we insert the single strand into a drilling hole and grout it to the anchor. After setting a hydraulic jack, we remove the epoxy coating at the end of the strand and pull out the embedded optical fiber. Then, an optical connector is attached using a fusion splicer for connecting an optical measurement instrument. The strain distribution along the anchor is measured during load testing and after anchoring. As a result, the stress distribution along the anchor is accurately measured in situ during construction and thus, these sensors have the potential to monitor soil conditions.