This study investigated the mechanical properties and antibacterial activity of glass ionomer cement (GIC) containing 1 mol% or 5 mol% gallium phosphate glass (GPG) powder. GPG were added to conventional GIC powder in a range of 0~20 wt%. The specimens for compressive strength (4 mmØ×6 mm) and diametral tensile strength (6 mmØ×4 mm) were prepared by mixing with the cement liquid and kept in an water of 37±1℃. Mechanical properties were evaluated at an interval of 1 h, 24 h, and 7 days. Antibacterial activity of specimens against to S. mutans and S. sobrinus was evaluated using agar diffusion methods. Data were statistically analyzed by one-way ANOVA and Tukey HSD post-hoc test (p<0.05). Diametral tensile strength of GIC containing GPG were significantly higher than control GIC while compressive strength showed no statistical difference. There was an increasing tendency of antibacterial activity for GPG-GICs. Results indicated that GPG can be considered as potential reinforcing agent for increasing antibacterial and mechanical properties for conventional GIC.