In a quest to develop effective methods for the elimination of organic pollutants and water remediation, a series of Fe3O4/ZnO/graphene composites are prepared and characterized. These composites are utilized as heterogeneous catalysts during the Fenton oxidation reaction for the degradation of the dyes, Congo red (CR) and methylene blue (MB), in aqueous solutions in the dark or under light and ultrasound, separately or simultaneously. The effects of various parameters, such as initial pH, H2O2 concentration, and graphene content, on the activity of the catalysts and, the iron leaching from the heterogeneous catalyst are investigated. The results demonstrate that all the catalysts exhibit excellent activities during the Fenton reaction under light and ultrasonic irradiation and that the incorporation of graphene significantly accelerates the MB and CR degradation. Complete elimination of CR and MB can be achieved in less than 1 h by simultaneous light and ultrasonic irradiation although CR was more effectively degraded as compared to MB. Moreover, the incorporation of graphene could reduce the leaching of iron ions from Fe3O4 to the solution. Thus, the Fe3O4/ZnO/graphene composite exhibits good stability after 4 repetitions of the cycling process.