The objectives of the study are to develop a prototype unit of photocatalytic reactor using UV light/TiO2 for mitigation of air emissions from swine buildings; and to determine effectiveness of the photocatalytic reactor in reducing multiple air emission constituents from a research nursery swine building, including H2S, NH3, N2O, CH4, and VOC. A five-stage honeycomb configuration is used for fabrication of the photocatalytic reactor. The reactor was tested in lab and in the field. In the lab test, when residence time was long (8 to 16 seconds), the reactor was able to significantly reduce H2S and NH3 at high concentration levels. In the field test, when residence time was short (0.018 to 0.042 seconds), the reactor can significantly reduce H2S and NH3 only at very low concentration levels. The amounts of reduction of H2S or NH3 per unit of residence time were comparable for different scales of residence time in the lab test and the field test. For H2S, the reductions were from 5.3 to 22.8 ppb per second of residence time. For NH3, the reductions were from 0.3 to 1.7 ppm per second of residence time. This information can be used for proper sizing of the photocatalytic reactor. The photocatalytic reactor had a side effect of increasing N2O concentrations. The effect of the photocatalytic reactor on VOC was not confirmed in our tests due to the limitation of the measurement instruments.