The object of the invention is to provide a penetration inhibiting method for sufficiently preventing the penetration of ink into a print medium even when the inkjet printing is performed to the print medium having a hydrophilic porous surface, and to provide a penetration inhibitor used in the method and a solvent ink containing the penetration inhibitor. As means to resolve the object, there isprovided a penetration inhibitor, to be added to an inkjet solvent ink for preventing the penetration of the solvent ink into a print medium, comprising an organic-solvent-soluble resin and inorganicfine particles.