Titanium dioxide (TiO 2) is one of the best semiconductor photocatalysts due to its high stability, oxidative power, nontoxicity, low cost etc. But its photocatalytic activity is limited due to rapid recombination of photo-generated electronhole pair, wide band gap and anatase to rutile phase transformation. These disadvantages can be eliminated by introducing dopants into the TiO 2 nanocrystals. Sol-gel and hydrothermal methods can be used for the synthesis of doped and co-doped TiO 2 nanocrystals. Advanced characterization techniques can be used for the study of phase structure, optical properties, thermal properties, surface area, morphological changes and photocatalytic activity of doped and co-doped TiO 2 nanoparticles. Doping inhibits the anatase to rutile phase transformation and suppresses the recombination of photo-generated electron-hole pair which enhances the photocatalytic activity. Here we made a review on the synthesis, characterization and photocatalytic activity of La, Ce doped and co-doped TiO 2 nanoparticles.