A Bi-2212 superconducting magnet with a practical room temperature (RT) bore of 45 mm diameter has been fabricated. The magnet was cooled by a Gifford-McMahon cryocooler and generated magnetic fields up to 0.68 T at 20 K. Oxide superconducting magnets with such a large RT bore require high homogeneity of the critical current density in the silver-sheathed Bi-2212 tape over long ranges such as 1500 m. This problem has been solved by optimizing the time for calcination of the Bi-2212 powder and employing a new heat process.