Abstract In recent years, recycled waste materials have been widely used to produce construction materials in an effort to reduce the utilization of natural resources and post-consumer wastes entering landfills. In this paper, the results of an experimental programme on studying the feasible use of spent fluorescent glass (FG) as a fine aggregate replacement in cement mortar are presented. Two types of FG were adopted in this study, one with (FG-A) and one without (FG-B) heating treatment at around 375 °C, to ensure the removal of mercury within the broken FG. The use of FG up to 40% to replace sand showed no obvious difference in density, but demonstrated an enhancement in workability and less shrinkage in the cement mortar. In comparison, the reduction of mechanical strength for a given content of FG-A usage in mortar is relatively lower than that of FG-B. This could be due to the FG-A (after the heating treatment) being free from the organic lacquer and the smooth coating, resulting in a better bond with the cement paste matrix. All the FG samples experienced big length changes due to the alkali-silica reaction (ASR), associated with their high solubility and the original microcracks present in the interior of the thin FG particles. The Toxicity Characteristic Leaching Procedure (TCLP) results indicated that utilizing of both FG-A and FG-B in the cement mortar could effectively reduce the leachability of mercury, from 12.99 mg/L and 70.55 mg/L (determined original FG-A and FG-B values before they were incorporated into the cement mortar) to below the permissible limit of 0.5 mg/L. However, the replacement ratio of FG should be limited to 30% or below.