Wang, LK, Wang MHS and Thayer, AE (2019). A spectrophotometrical method for determination of dissolved proteins in water or wastewater. In: “Evolutionary Progress in Science, Technology, Engineering, Arts, and Mathematics (STEAM)”, Wang, Lawrence K. and Tsao, Hung-ping (editors). Volume 1, Number 12, December 2019; 57 pages. Lenox Institute Press, Newtonville, NY, 12128-0405, USA. No. STEAM-VOL1-NUM12-DEC2019; ISBN 978-0-9890870-3-2. ————— ABSTRACT: The objective of this research are two-fold: (a) to review current methods for rapid analysis of dissolved protein in water and wastewater: and (b) to introduce a new spectrophotometrical method for determination of dissolved proteins in the 10-2500 mg/L range using carbonate-tartrate reagent, phosphomolybdic-phosphotungstic reagent, and copper sulfate. The new analytical method is a colorimetric determination based on the reaction of dissolved protein, specifically the peptide bonds and the amino acids tryptophan and tyrosine with the authors suggested reagents. Two reactions are necessary:(a) The reaction between the protein molecules and copper ions in an alkaline solution; and (b) The reduction of a phosphomolybdic phototungstic reagent by the copper treated protein. The optical density of treated dissolved protein is then determined at 400-700 nm range using a spectrophotometer with 1 cm light path or longer. With certain modification, this method may also be used in the field using the calibration curves prepared in the laboratory.