Introduction: Glass ionomer cement (GIC) has numerous advantages over other restorative materials. In particular, self-adhesion to tooth structure in addition to its fluoride release that makes it suitable for treatment of majority of high caries risk cases. However, clinical usage of GIC is still limited due to their sensitivity to initial desiccation, low resistance to abrasion and low esthetic properties explaining why these materials are not widely used for permanent fillings. Materials and Methods: Class II occlusal slot cavities were prepared in the first permanent molar of sixty patients and restored randomly by two restorations, either; EQUIA® Forte Fil (Glass ionomer with glass hybrid technology) or Zirconomer® Improved (Zirconia-reinforced glass ionomer). Restorations were evaluated according to FDI criteria in terms of biological properties at baseline, after six months and one year. Results: Chi-square and Mann-Whitney tests revealed that there was no statistically significant difference between both materials with 100% success in all restorations in both groups at the base line. At six months follow up time, 92% of the EQUIA®Forte Fil group and 68% of the Zirconomer® Improved group were clinically successful. Meanwhile, at 12 months follow up time, 88% of the EQUIA®Forte Fil group and 48% of the Zirconomer® Improved group were clinically successful with significant difference between them at both six and 12 months. Conclusions: Glass ionomer with glass hybrid technology exhibited better clinical performance in terms of biological properties than zirconia-reinforced glass ionomer in class II slot cavities after six months and one year