A multi-color ink for 3D printing, a 3D printer, and a method of controlling the 3D printer are provided. The multi-color ink for 3D printing including a first ink composition that includes a photocurable material, a photoinitiator configured to cure the photocurable material, a first colorant, and an anti-intercolor bleed agent configured to prevent intercolor bleeding occurring when the plurality of ink compositions come into contact with each other, and a second ink composition that includes a photocurable material, a photoinitiator configured to cure the photocurable material, and a second colorant having an acid moiety involved in a reaction with the anti-intercolor bleed agent to cause aggregation. The multi-color ink for 3D printing may enable a clear image by inhibiting intercolor bleeding that occurs when ink compositions with different colors are printed to be adjacent to each other before curing during 3D printing.