This study is to determine the effect of wastewater disposal from the Warri Refinery and Petrochemical Company (WRPC) on the DNA integrity in the African catfish, Clarias gariepinus juveniles exposed to 1, 10, 20 and 30 % (v/v) of the wastewater. The Random Amplification Polymorphic DNA (RAPD) technique was employed to evaluate the level of DNA alteration in the fin tissue extracted by a modified salt extraction method followed with PCR amplification. Polymorphism became more evident as the presence and/or absence of DNA fragments treated samples and compared with the control. DNA polymorphism was reflected by changes in the RAPD profiles as variation in band intensity, disappearance of bands and appearance of new bands induced by the different concentration of wastewater on the genome of the aquatic organism. A total of 57 RAPD bands were obtained using four oligonucleotide random primers and 32 (56%) of these fragments showed polymorphism. The loss and gain of bands decreased with increase of waste water concentration. There was a distinct distance between the band patterns of treated organism and the control sample when cluster method was applied. The genetic distance shown on the dendrogram revealed that genotoxicity of the wastewater was also concentration-dependent.