A composite cement made of strontium containing tricalcium silicate and hydroxyapatite (SrC₃S/HAp) was prepared and studied through a two-stage sol–gel method. The elemental components are 75 wt% of strontium-doped tricalcium silicate (SrC₃S) and 25 wt% of hydroxyapatite (HAp). According to previous studies, the SrC₃S has good mechanical properties and hydraulic conductivity, and the HAp has good biocompatibility. Therefore, the 75SrC₃S-25HAp powder with 10 wt% of NaH₂PO₄ solution was mixed to prepare the slurry material. This slurry was measured for the working time and setting time at 37 °C under saturated vapor pressure. The material properties were evaluated in terms of crystal structures, surface morphologies, and mechanical properties. The in vitro testing was conducted to determine the ion release rate and curing behavior under a simulated body fluid environment. Finally, the L929 murine fibroblast cells were cultured to study the biocompatibility of the material. The results indicated that the operating time was 15.2 min, and the setting time was 43.6 min. After being soaked into simulated body fluid for14 days of the experiment, the compressive strength of 75SrC₃S-25HAp remained 22.1 MPa, and the release of calcium and strontium ions was 501.4 ppm and 49.5 ppm, respectively. The cell viabilities were higher than 70% in various concentrations. These results suggest the 75SrC₃S-25HAp has excellent potential for bone cement application.