(219774) 2001 YY145 is a stony asteroid and exceptionally slow rotator from the inner regions of the asteroid belt, approximately 1.5 kilometers in diameter. It was discovered on 18 December 2001, by the U.S. Lowell Observatory Near-Earth-Object Search (LONEOS) at Anderson Mesa Station near Flagstaff, Arizona. The Collaborative Asteroid Lightcurve Link assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 1.54 kilometers, based on an absolute magnitude of 16.43.