To provide an ultraprecise magnetic polishing method capable of attaining highly precise polishing of a pipe inner surface and easy cleaning and to provide a polishing slurry for ultraprecise magnetic polishing.

Using a pipe 1 to be polished, polishing slurry 2 introduced into the pipe 1 to be polished and a pipe inner surface magnetic polishing apparatus 3 for agitating the polishing slurry 2 by relatively moving the pipe 1 to be polished and the polishing slurry 2, the inner surface of the pipe 1 to be polished is polished with the polishing slurry 2 by moving the pipe inner surface magnetic polishing apparatus 3. At this time, the polishing slurry 2 comprises spherical magnetic particles, polishing particles having average particle diameter in the range of 1/4 to 1/1000 of the average particle diameter of the magnetic particle, and a slurry medium which is a medium for making the magnetic particles and the polishing particles into a slurry state and does not contain additive for dispersing the polishing particles in the polishing slurry.