The regeneration of bone lost due to disease and trauma as well as the bonding of bone to biomedical implants present significant challenges to the field of biomaterials. Increasing evidence for the benefit of strontium as a potent anti-osteoporosis therapy suggests that biomaterials which can release strontium to the surrounding environment may find a range of uses in orthopaedic, spinal and dental surgery to regenerate hard tissue. Here we report on the structure and physical properties of a series of ten glasses based on 45S5 Bioglass®, where 0 to 100% of the calcium was substituted with strontium on a molar basis. Characteristic temperatures were determined using differential thermal analysis. We also analysed the structure of the glasses with Raman spectroscopy and assessed their cytotoxicity using a human osteosarcoma cell line. All characteristic temperatures (except crystallisation onset, T_x) decreased with strontium addition to the glass. Glass molecular structure did not change across the series and the silicate network was predominantly composed of linear chains (Q²) and a small amount of (Q³) with isolated orthophosphate units (Q⁰). The phosphate was present as [PO₄]³⁻ orthophosphate units (Q⁰) in all glasses. Immersion of the Sr-glasses in simulated body fluid (SBF) showed formation of biomimetic apatite in 1 week or less. Cell proliferation assays demonstrated that all the glass compositions supported normal cell attachment and proliferation. In summary, we show that strontium can be added to bioactive glasses in place of and in combination with calcium with minimal alteration to glass physical properties. These strontium-substituted bioactive glasses will be useful for a range of applications in orthopaedic regenerative medicine.