The unique property of phosphate-based glasses and fibres to be completely dissolved in aqueous media is largely dependent on the glass composition. This article focuses on investigating the effect of replacing NaO with 3 and 5 mol% FeO on cytocompatibility, thermal and dissolution properties of PO-CaO-NaO-MgO-BO glass system, where PO content was fixed at 45 mol%. The effect of increasing FeO from 3 to 5 mol% on PO-CaO-NaO-MgO glasses was also evaluated. The glass transition temperature, onset of crystallisation temperature and liquidus temperature were found to decrease with increasing FeO content and the addition of BO, while the thermal expansion values were found to decrease. The density of the glasses decreased with increasing FeO content. However, an increase in the density was observed by the addition of 5 mol% BO. The dissolution properties and mode of bulk glass and fibres were also examined which were found to decrease with increasing BO and FeO. However, it was found that the dissolution properties of the glasses containing both BO and FeO were lower than only FeO containing glasses. The in vitro cell culture studies using human osteoblast like (MG63) cell lines revealed that the glasses containing both BO and FeO maintained and showed higher cell viability as compared to the only FeO containing glasses. Glasses containing both BO and FeO showed a pronounced effect on the dissolution rate of the glasses, which eventually improved the cytocompatibility properties of the glasses investigated.