This study introduces a sustainable 3D printing technique using a reversible salting-out effect with aqueous salt solutions. The salting-out effect, induced by salt solutions, lowers the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) solutions to below 10 °C, enabling spontaneous and instant physical crosslinking within PNIPAM chains at room temperature. This allows PNIPAM solutions to solidify upon contact with a salt solution, without the need for rheological modifiers, chemical crosslinkers, or additional post-processing steps. The technique is applicable to various PNIPAM-based composite solutions, incorporating functional materials or other polymers, and demonstrates potential for developing water-soluble disposable electronic circuits, carriers for delivering small materials, and smart actuators. The reversible physical crosslinking and de-crosslinking of the polymer through the salting-out effect also enable the recyclability of the polymeric ink, making it a simple and sustainable 3D printing approach.This study introduces a sustainable 3D printing technique using a reversible salting-out effect with aqueous salt solutions. The salting-out effect, induced by salt solutions, lowers the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) solutions to below 10 °C, enabling spontaneous and instant physical crosslinking within PNIPAM chains at room temperature. This allows PNIPAM solutions to solidify upon contact with a salt solution, without the need for rheological modifiers, chemical crosslinkers, or additional post-processing steps. The technique is applicable to various PNIPAM-based composite solutions, incorporating functional materials or other polymers, and demonstrates potential for developing water-soluble disposable electronic circuits, carriers for delivering small materials, and smart actuators. The reversible physical crosslinking and de-crosslinking of the polymer through the salting-out effect also enable the recyclability of the polymeric ink, making it a simple and sustainable 3D printing approach.