Department of Chemistry, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata-700 009, India E-mail : debarshan@scientist.com National Institute of Research on Jute and Allied Fiber Technology (ICAR), 12, Regent Park, Kolkata-700 040, India Manuscript received online 23 July 2013, revised 21 October 2013, accepted 28 October 2013 At normal laboratory temperature and atmospheric pressure, experiment on waste water containing metanil yellow by photo-Fenton process were conducted to examine the effect of operating variables like the concentration of ferric ion, concentration of metanil yellow, pH, hydrogen peroxide and light intensity on the reaction rate. Metanil yellow was completely oxidized and degraded into CO2 and H2O in this experiment. A mechanism for photochemical bleaching of metanil yellow by photo-Fenton’s reaction has been processed.