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The objective of this study was to evaluate the effect of the addition of synthesized hydroxyapatite (HA) and fluorapatite (FA) nanoparticles to a glass-ionomer cement (GIC) on the mechanical properties, while preserving their unique and potent clinical properties. Bioceramics, such as HA and FA, have been recognized as restorative materials (e.g. GICs) in dentistry due to their chemical and biological compatibility with human hard tissues, which are considered calcium phosphate complexes. In this study, both of these inorganic nanoparticles (HA and FA) were synthesized via a wet-chemical precipitation method. The obtained nanoparticles were characterized with X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) Theory. Then, HA and FA were incorporated into the powder component of the resin-modified cement (Fuji II, GC gold label, GC international, Tokyo, Japan) at 5% and 8 wt%, and unblended powder was employed as control. Compressive strength (CS) and diametral tensile strength (DTA) before and after 1, 7 and 28 days of storage in distilled water were evaluated using a universal testing machine. Surface microhardness after 1 and 7 days of storage in distilled water was determined using Vickers microhardness tester. Setting and working time was measured as specified in the ASTM standard. The surface morphology of the modified GICs was examined using SEM observations. The morphology of the synthesized HA and FA nanoparticles was hexagonal, and their average sizes were about 25 nm and 30 nm, respectively. The mechanical results of the modified GICs ascertained addition of HA and FA (5 and 8 wt%) into the glass ionomer cement after 7 days of storage in distilled water exhibited statistically higher CS of about 107–113.6 MPa and 111–117.8 MPa, respectively, and also higher DTS, 13–16 MPa and 14–19 MPa, respectively. The hardness of the glass ionomers containing HA and FA nanoparticles (5 wt%) were increased by 2.21% and 11.77%, respectively. In addition, working time and setting time by adding the 5% nanoparticles were reduced about 8.5% and 13.23% for HA and 10.63% and 19.11% for FA, respectively. It was concluded that glass ionomer cements containing nanobioceramics (HA and FA) are promising restorative dental materials with improved mechanical properties. These experimental GICs may be potentially employed for higher stress-bearing site restorations, such as Class I and II restorations. [ABSTRACT FROM AUTHOR]