Poly dopamine coated iron oxide nanoparticles (FeO@PDA NPs) were synthesized, characterized, and their MR imaging contrast agents and photothermal potency were evaluated on melanoma (B16-F10 and A-375) cells and normal skin cell. To this end, MTT assay, Fe concentration, and MR imaging of both coated and uncoated NPs were assessed in C57BL/6 mice.Fe3O4 nanoparticles were synthesized using co-precipitation, and coated with poly dopamine. The cytotoxicity of FeO and FeO@PDA NPs on melanoma cells with different concentrations were obtained using MTT assay. MR images and Fe concentration, of nanoprobe and nanoparticles were evaluated under in vivo conditions.Findings indicated that uncoated FeO showed the highest toxicity on animal (B16- F10) cells at 450µg/ml after 72h, while the highest toxicity in human (A-375) cells were observed at 350µg/ml. These nanoparticles did not reveal any cytotoxicity to normal skin cells, despite having some toxicity features in A-375 cells. MR image signals in tumor were low compared with other tissues. The iron concentration in tumor was higher than that of other organs.It is concluded that the cytotoxicity of FeO@PDA were found to be significantly lower than uncoated nanoparticles (p <0.001) which allow some positive effects on reducing toxicity. The prepared nanoprobe may be used as contrast agent in MR imaging.