THE INDUSTRIAL DYES ARE ONE OF THE MOST POLLUTANT COMPOUNDS. SOME OF THE INDUSTRIAL DYES ARE TOXIC AND MAY CAUSE THE CARCINOGENIC EFFECTS [1-2]. ON THE OTHER HAND THESE DYES HAVE WIDELY BEEN USED IN TEXTILE, COSMETIC, FOOD COLORANTS, PRINTING, AND PHARMACEUTICAL INDUSTRIES. THEREFORE DYES ESPECIALLY AZO DYES HAVE BEEN FOUND TO BE VERY HARMFUL FROM THE ENVIRONMENT POINTS OF VIEW. IN RECENT YEARS, ENVIRONMENTALLY CHEMISTS HAVE PRESENTED A VARIETY OF METHODS FOR REMOVAL OF NON-PLEASANT CHEMICALS INVOLVING PHYSICAL ADSORPTION [3], ADVANCE OXIDATION PROCESSES [4-6], BIOSORPTION [7] AND ULTIMATELY PHOTOCATALYTIC PROCESSES. ONE OF THE EFFECTIVE WAYS FOR POLLUTANT REMOVAL IS PHOTOCATALYTIC DEGRADATION THAT USES ULTERA VIOLET LIGHT AND SEMICONDUCTOR AS EFFECTIVE AGENTS. THE AIM OF SEMICONDUCTOR PHOTOCATALYSIS IS TO EFFECTIVELY DETOXIFY ORGANIC POLLUTANTS. IN THIS RESEARCH, PHOTOCATALYTIC DEGRADATION OF YELLOW PYOCTANINE DYE WERE INVESTIGATED IN THE PRESENCE OF NANO-POWDER ZINC OXIDE AT BUFFER AND NON-BUFFER PHS UNDER 400 W HIGH PRESSURE MERCURY LAMP UNDER AEROBIC CONDITIONS AT ROOM TEMPERATURE. THE EFFECTS OF UV LIGHT, BUFFER AND NON-BUFFER PHS, IRRADIATION TIME AND NANO-POWDER ZINC OXIDE WERE STUDIED.THE PHOTOCHEMICAL DEGRADATION OF DYE WAS FOUND TO BEHAVE AS A FIRST ORDER REACTION. KINETIC INVESTIGATION OF PHOTODEGRADATION OF YELLOW PYOCTANINE DYE, SHOWED THAT THE REACTION OBEY FROM IMPROVED LANGMUIR-HINSHELWOOD (L-H) MODEL.USING THIS MODEL,OBSERVED RATE CONSTANT AND LANGMUIR- HINSHELWOOD ADSORBTION CONSTANT WERE DETERMINED.