Diatomite supported nano-TiO2 composite was prepared by sol-gel method with titanium (Ⅳ) isopropoxide as precursor. The composite was characterized by XRD, SEM and FT-IR. The TiO2 coated on the surface of diatomite was the mixed crystal of anatase and rutile, the average particle size was 11 nm. The photocatalytic activity of composite was larger than that of the Degussa P25-TiO2. The stability of TiO2/diatomite was good and the photocatalytic activity reduced only 12.4% after repetitive-use the catalyst for 15 times.