The development of ion-releasing resin composites is expected to reduce the risk of secondary caries. This study compared the degree of monomer conversion, biaxial flexural strength/modulus, elemental release, and remineralisation potential of a novel ion-releasing dental composite (Renewal MI) containing monocalcium phosphate monohydrate and polylysine. The degree of monomer conversion after light curing for 20 s was determined (n = 8). The biaxial flexural strength and modulus after immersion in water for 24 h (n = 8) were evaluated. Additionally, the release of Ca and P after immersion in water for 2 weeks was assessed (n = 3). A disc specimen of the material (n = 1) was attached to the demineralised dentine and then immersed in simulated body fluid for 2 weeks to qualitatively determine mineral precipitation on dentine. The commercial comparison included Filtek Z350 XT, EQUIA Forte HT, FUJI VII, and FUJI II LC. FUJI II LC demonstrated the highest degree of conversion (97.6%) compared to Renewal MI (57.2%) and Filtek Z350 XT (61.2%). The highest flexural strength was observed in Filtek Z350 XT (271 MPa), followed by MI (135 MPa), FUJI II LC (109 MPa), EQUIA Forte HT (50 MPa), and FUJI VII (35 MPa). The biaxial flexural modulus of Renewal MI (3.2 GPa) was comparable to that of EQUIA FORTE HT (3.8 GPa) and FUJI II LC (3.6 GPa). Ca and P release of MI (11 ppm, 45 ppm) was higher than that of FUJI VII (<0.1 ppm, 0.7 ppm). The precipitation of mineral precipitates in dentinal tubules of demineralised dentine was not detected in all materials. Renewal MI demonstrated a degree of conversion similar to commercial resin composite but exhibited lower strength. However, its strength was much higher than conventional glass ionomer cements. The material promoted the high release of elements, which was expected to encourage the remineralising actions.