A simple UV/UV-visible method is described for the determination of global nitrogen and total phosphorus in wastewater. This method includes two steps: first, the photo-oxidation of nitrogen and phosphorus forms into nitrate and orthophosphate ions, and their quantification by UV-visible spectrophotometry. Potassium peroxodisulfate is used as oxidant. The developed system consists of on-line association of UV photo-oxidation reactor with UV-visible detector. The conversion yields vary between 80 and 100% for both nitrogen compounds (ammonium, urea, amino acids, and other N-containing compounds), and phosphorus compounds (ADP, ATP, and other P-containing compounds). The time requires for nitrogen and phosphorus forms determination is no longer than 20 min.