Soil nailing technology has been commonly used for upgrading geotechnical structures such as retaining walls, excavations orslopes,etc. The reinforcing effect of a soil nail in the geotechnical structures is largely related to the soil nail cement grout quality, which ishowever invisible while the soil nail is installed inside the geotechnical structures. This paper presents a study on the cement grout quality ofmodel soil nails measured using Long Gage fiber Bragg grating (FBG) sensing technology and by carrying a pullout test. In this study, aseries of pullout tests were performed for model soil nails grouted with various cavity defects. Long-Gauge FBG (LGFBG) sensing array wasthen used for measuring the strain distributions along the model soil nails. Test results indicate that the presence of cavity defects due to poorgrouting quality can be identified within a specific range by using the LGFBG sensing array