The photocatalytic activity was significantly changed by the modification of folic acid. Methylene blue solution was used for the determination of TiO2 activities before and after the coupling of folic acid. Based on first 300 s data, the rate constants were calculated to be 0.0073 s−1, 0.0044 s−1 and 0.002 s−1 for folic acid-modified TiO2 with FA-to-TiO2 ratios of 0.2, 0.5 and 1, respectively. In comparison with unmodified TiO2having a rate constant (k) of 0.0104 s−1, the conjugation of folic acid led to the decrease of photocatalytic activity of TiO2. The binding of folic acid apparently obstructed the access of methylene blue to TiO2.