With the aim to reinforce mechanical properties of glass ionomer cements (GICs), basalt fibers (BF, Ф13.3 μm) with 1 mm and 2 mm length were added into glass powders of commercial self-cure GIC Fuji IX with a series of mass fraction to prepare BF reinforced GICs. Fuji IX without BF was used as control. The influences of BF fibers length and mass fraction on flexural strength (FS), flexural modulus (FM), compressive strength (CS) and fracture toughness (FT) were investigated. The results showed that BF could reinforce mechanical properties of GIC significantly (p < 0.05), and the BF reinforced GIC with 7 wt.% (mass ratio in glass powders of GIC) of 2 mm fibers had the optimal mechanical properties in this research. Water sorption (WS), solubility (SL), and flexural properties after water aging of optimal BF reinforced GIC were then investigated and compared with control GIC. The FS of BF reinforced GIC decreased with the increasing of water aging time (p < 0.05), and became comparable with that of control GIC after 1 month of aging time (p > 0.05), while FMs of BF reinforced GIC and control GIC were comparable with each other (p > 0.05) and had no variation after water aging (p > 0.05). The WS of BF reinforced GIC was higher than that of control GIC (p < 0.05), but there was no significant difference in SL between these two GICs (p > 0.05). In conclusion, BF could be used to reinforce GIC, but the weak interaction between fibers and cement matrix would influence its long-time serving properties, thus further study concerned about increasing interaction between fibers and cement matrix should be taken.