To elucidate the possibility of practical use of dye-sensitized solar cells (DSSCs) in Building Integrated Photovoltaics (BIPV) application, outdoor test has been carried out for over four years. This is almost the longest outdoor test of DSSCs. Performances of DSSCs prepared with two different kinds of dyes are tested. DSSCs with dye Z991 generate about 15% more electricity yearly than those with dye Z907 in the first two years and then the gap is widening because of the better stability of dye Z991. Efficiency of DSSCs with dye Z991 decreases 17% at the first two years and then becomes stable, while DSSCs with dye Z907 are out of use after 4-year outdoor testing. For BIPV use, Pm.,, increases with the solar Irradiance Pi and gets the highest value around 12:00, while the efficiency is almost unchanged from 8:00 to 16:00 as the sun moves. The output of DSSCs increases not linearly with the irradiance, especially under irradiance lower than 20 Wh, implying that efficiency measured under AM1.5G conditions is not a crucial indicator to evaluate the performance of DSSCs. The total energy yields of DSSCs throughout the years are slightly higher than that of pc-Si cell with the same installed capacity, and DSSCs generate 15-20% more electricity from May to August when temperature is higher and irradiance is lower. The results show potential application in outdoor BIPV, especially in hot and humid climate, although larger exposed area is still required to attain the same installed capacity with pc-Si cell.