The present study evaluates the photocatalytic degradation of congo red as a model of organic pollutant over LaFe- and CeFe-codoped ZnO nanoparticles under UV light irradiation. Both photocatalysts were synthesized using co-precipitation method and characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, diffuse reflectance spectroscopy. The photodegradation efficiency of congo red using two 20W UV lamp was higher for LaFe-codoped ZnO nanoparticles compared with CeFe-codoped ZnO nanoparticles. Photocatalytic mechanism was investigated by measuring the photocatalytic degradation rate in the presence of ammonium oxalate, natrium sulfate, tert-butyl alcohol as photogenerated holes, photogenerated electrons and hydroxyl radical species scavenger. The results revealed that electrons are the main species in the photocatalytic process.