SrTiO3 nanocube and three dimensional, mesoporous BiOBr catalysts were synthesized by sol-gel and precipitation methods respectively. Various weight percentages of SrTiO3-BiOBr heterojunction composite catalysts (x% SrTiO3-BiOBr where x= 5, 10, 30, 50 & 70 percentage of SrTiO3) were synthesized by impregnation method. All the synthesized catalysts were characterized by various instrumental techniques. The results of PL and EIS indicate that the heterojunction catalyst, 10% SrTiO3-BiOBr (10-ST/BB), has the lowest recombination rate of e(-)-h(+) pairs and the lowest electron transfer resistance respectively. Photocatalytic activities of the synthesized catalysts were tested towards the degradation of carcinogenic reactive dyes such as reactive blue 198, reactive black 5 and reactive yellow 145 in presence of visible and solar irradiations. Among the catalysts 10-ST/BB resulted in the highest photocatalytic activity towards the degradation of all the three dyes. Kinetics studies on degradation indicated that it followed pseudo first order. The efficiency of dye degradation was found to be better in the presence of solar light than under visible light degradation due to similar or equal to 4% UV light in solar irradiation. TOC, HPLC and COD studies confirm that the dyes are mineralized into some organic salts such as acetates, formates, etc., CO2, water and salts. (C) 2017 Elsevier B.V. All rights reserved.