A large relative surface area is crucial for high catalytic activity. Monolithic catalysts are important catalytic materials because of minimal self-degradation. Regarding large surface area catalysts, the glass-ceramics (GCs) with high formability, obtained by heat-treatment of the precursor glass, are plausible candidates. This study examines the photocatalytic behaviour of porous GCs obtained after acid leaching of MgO-TiO2-P2O5 GCs. After heat-treatment, anatase TiO2 was precipitated along with other phases. The diffraction intensity ratio between anatase and other phases was the maximum for a heat-treatment temperature of 900 °C. After acid leaching of the GCs, the relative surface area decreased with increasing TiO2 fraction; the surface area was also affected by the sample morphology. H2 generation was observed from porous GCs, while GCs without etching exhibited approximately zero activity. Thus, it was demonstrated that high surface area and prevention of the reduction reaction to Ti(III) are important for tailoring monolithic photocatalytic materials.