An in-vivo intravascular blood replacing liquid of the present invention is injected into a blood vessel to replace blood at an intravascular portion to be inspected therewith in making an in-vivo intravascular inspection. The blood replacing liquid comprises an aqueous medium unharmful for a living body and a gelling property imparting substance, unharmful for the living body, which is added to the aqueous medium to impart a gelling property to the blood replacing liquid. The blood replacing liquid has a viscosity of not more than 3 mPa·s when the blood replacing liquid is injected into the blood vessel.
