Gallium and yttrium co-doped BaZrO3 based proton conductors sintered at 1600°C, in which total dopant concentration is fixed at 15mol%, are fabricated using the conventional solid state reaction method. Ga concentration dependence on sinterability and electrical properties are evaluated. Lattice parameter a, relative density and grain size show local maximum at 1mol% Ga concentration, i.e. BaZr0.85Y 0.14Ga0.01O2.925 (BZY14Gal). Relative density of it is over 95%. It is also found that grain boundary conductivity is drastically improved by 1mol% Ga additives. But bulk conductivity becomes slightly lower than that of BZY15 by 1mol% Ga additives. However, total conductivity of BZY14Gal is highest in the specimens due to high grain boundary conductivity and the value is over 2 x 10-3 Scm-1. On the other hand, 3 and 5mol% Ga-doped specimens show significantly low bulk and grain boundary conductivity. So, the results suggest that the Ga additive is effective for sintering at 1600°C, but the range of concentration is very limited.