Gypsum-based building materials consisting of (i) waste gypsum recovered via flue-gas desulfurization or (ii) com. gypsum were modified by addn. of TiO2 photocatalyst. The (i) and (ii) samples with various TiO2 content (1-10% by mass) were studied for photocatalytic activity in NO degrdn. and mech. properties (compressive strength under dry and wet conditions). Firstly, the TiO2 presence in gypsum matrix resulted in NO photocatalytic degrdn. (40.4-67.9% and 34.1-63.5% for (i) and (ii), resp.), increasing with TiO2 loading. Secondly, the TiO2/gypsum mass ratio 2-3% did not influence significantly on compressive strength. Thirdly, using (i) provided better results in comparison to (ii), in both photocatalytic and mech. properties. The optimum mixt. was (i) with 3% by mass of TiO2 (58% NO degrdn.). It had higher compressive strength than the unmodified (ii) (9.44 vs. 8.83 and 3.02 vs. 2.92 under dry and wet conditions, resp.) and a longer lifecycle time.