Co(II) and Se(VI) were not removed with conventional biological treatments, adsorption and chemical processes. Graphene oxide and mangane are excellent adsorbent for heavy metal remediation since their negative surface charge at an alkaline pH. Therefore, in this study, by doping the mangane oxide to the the graphene oxide Co(II) and Se(VI) were removed. XRD pattern of graphene oxide-mangane oxide samples showed that this nanocomposite exhibits poor cristallinity and contained MnO in Birnessite form. EDS analysis results showed that the graphene oxide has the lowest surface area (32 m2/g) and pore volume (0.11 cm3/g) with an average pore size of 17.3 nm. As the pH was increased from 2,0 to 9,0; the negativity of the zeta potantial of graphene oxide- mangane oxide nanocomposite decreased. Tthe narrow O 1s XPS spectra of mangane oxide-graphene oxide nanocomposite contained MnO2.The FTIR spectra of the nanocomposite showed that hydroxyl and carboxyl groups were present. For maximum Se(VI) and Co(II) adsorptions (98% and 98%); the optimum graphene oxide–mangane oxide concentration was found as 4 mg/L, at a pH of 8.9 at 21 0C after 20 min contacting time. The adsorption of Co(II) and Se(VI) was explained by the pseudo-first order kinetic model while the maximum adsorption capacities of Co(II) and Se(VI) were 256 mg/g and 289 mg/g, respectively. Graphene oxide–mangane oxide nanocomposite was reused with the percentages of 86% and 90% for Co(II) and Se(VI), respectively after four sequential utilisation. This, reduce the treatment cost by 48% for Se(VI) and by 43% for Co(II).