The influence of selenium dioxide on bioglass in (45.0-x) SiO2 24.5Na2O 24.5CaO 6.0P2O5 xSeO2 (x = 0.0, 0.5, 1.0, 1.5, and 2.0 wt%) system was investigated by preparing the glass through conventional melting and annealing method. The glass transition temperature (Tg), crystallization temperature (Tc), and density of prepared glasses were measured by differential thermal analysis and Archimedes’ principle respectively. The structural and microstructure analyses of glasses were characterized by Raman spectroscopy, Fourier transformed infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). The formation of hydroxy apatite carbonate (HCA) layer for glasses was investigated by Raman spectroscopy, FTIR, SEM with EDS, pH measurement, ion concentrations analysis, and (%) weight loss after immersion in simulated body fluid (SBF) for 10 h to 14 days at 37.5°C. Experimental results showed that SeO2 substitution for SiO2 in the glass had increased glass density and molar volume whereas network connectivity was decreased. The addition of selenium oxide reduced the glass transition temperature and also crystallization temperature. The FTIR study of glass confirmed the P–O bonding after immersion for 14 days in SBF, which was also identified in the Raman spectroscopy. SEM of the 14 days immersed sample showed the formation of cauliflower like morphology of HA particles on the glass. pH and ion concentrations analysis also confirmed the formation of HCA layer after 14 days of immersion in SBF. © 2020, Australian Ceramic Society.