Contamination of water resources to heavy metals is a crucial environmental concern due to its toxicity effects on ecosystems and human health. This study focuses on the development of an efficient green nanosorbent for the selective adsorption of Ni (II) from Cr (VI) ions in aqueous solutions using phycocyanin-functionalized magnetic nanosorbents (PC-nanosorbent). This approach gains a potential for the recovering of these heavy metals from industrial effluents and reuse them. The adsorption experiments revealed a monolayer adsorption carried out between the ions and functional groups in the nanosorbents. The PC-nanosorbent showed higher efficiency for Ni(II) removal whereas Cr(VI), confirming a selective adsorption of these metals. Kinetic modeling indicated that the pseudo-second-order model best described the adsorption processes of these metals on the PC-nanosorbents, and a faster adsorption kinetics for Ni(II) compared to Cr(VI) was observed. Also, the Langmuir adsorption coefficients were qmax = 19.16 mg g-1 and KL = 0.0023 L mg-1 for Ni (II), and qmax =14.45 mg g-1 and KL = 0.2039 L mg-1 for Cr (VI). Furthermore, regeneration tests over three cycles showed good reusability, with a maximum capacity decrease of 16%. The results of this study indicate the potential of magnetic nanosorbents as a selective, efficient, feasible, and reusable technique for the selective adsorption of nickel from chromium ions in aqueous environments.