Optical Variability of Blazars

Variability is one of the characteristics of blazars. The rapid variability is superposed on the long term variations. In this talk, the variability on different time scales, such as intra-day(IDV), short-term (STV), and long-term (LTV) variations are presented for some sources. For objects with many observations, we have made periodicity analysis, the results show that the long-term variation periodicity is in a range of about 1.4 to 18 years from our consideration. Some possible mechanisms for different time scales are also discussed. The optical polarization is correlated with the variation amplitude.