Fluoride-contaminated groundwater is mainly due to the release of fluoride from geological minerals and leakage of fluoride-contained industrial wastewater. The application of in situ long-lasting chemical adsorption remedial scheme could be a cost-effective approach for the treatment of the fluoride-contaminated groundwater to meet the remediation and risk control goals. In this pilot-scale study, the Mg-based (magnesium oxide, MgO) adsorbents [granulated magnesium oxide aggregates (GA-MgO) and surface-modified MgO powder (SM-MgO)] were developed to remediate a fluoride-contaminated groundwater site. MgO has the advantages of strong affinity, non-toxicity, and low price, and the use of MgO as an adsorbent can be applied in the broader pH environment. Results show that both GA-MgO and SM-MgO had porous, spherical, and crystal structures, and the specific surface areas increased from 4.2 m²/g to 201.8 and 215.6 m²/g after modification, respectively. Results from the adsorption kinetics indicate that the quasi-second-order dynamic adsorption model and the Freundlich isotherm adsorption equation could be applied to describe the chemical adsorption phenomena between fluoride and adsorbents. Results from the pilot-scale study show that fluoride concentrations in site groundwater dropped from 9.5 to below 3.3 mg/L after 7 days of SM-MgO supplement around the adsorbents injection area. Results demonstrate that SM-MgO can be used for cases of risk reduction and emergency response, and GA-MgO can be used for a long-term migration control of a fluoride plume. The treatment scheme would be expected to provide a more cost-effective alternative to remediate fluoride-contaminated groundwater. The remedial scheme has the potential to be further modified to cleanup heavy-metal contaminated sites.