B-band measurements of 3C 273 over some 110 years are compiled and used in a search for periodicities using the Jurkevich method. Periods of 2.0,13.65±0.20 and 22.5±0.2yr are found. If the long-term periodicity is from the instability of a slim disk, then the periodicity (～ 13-yr or ～ 22-yr) suggests masses of 107M⊙ for the central black holes.
Rui-Guang Lin (Center for Astrophysics, Guangzhou University, Guangzhou 510400) E-mail: lin_rg@163.net
