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The effects of temperature and concentration on the flow behavior and viscosity of nanofluids containing TiO 2 nanoparticles, pristine MWCNTs, oxidized MWCNTs and decorated MWCNTs with TiO 2 nanoparticles are experimentally investigated. The results of rheological characteristics of nanofluids revealed that nanofluid of TiO 2 nanoparticle and MWCNT-TiO 2 exhibits shear thickening or dilatant behavior. In contrast, nanofluids containing pristine and oxidized MWCNTs depict the shear thinning or pseudoplastic behavior. Also results demonstrated that the rheological characteristics of nanofluids are functions of temperature and concentration, whereas the viscosity of all prepared nanofluids decreases with increasing the temperature and decreasing the concentration. In addition, the results show that the oxidation of MWCNTs in nitric acid leads to the reduction in viscosity. The rheological behavior of decorated MWCNTs illustrates that viscosity decreases by increasing the attached TiO 2 nanoparticles. TEM results show that TiO 2 nanoparticles successfully attached to the outer surface of oxidized MWCNTs.