This paper is concerned with quantitative homogenization of second-order parabolic systems with periodic coefficients varying rapidly in space and time, in different scales. We obtain large-scale interior and boundary Lipschitz estimates as well as interior C 1,α and C 2,α estimates by utilizing higher-order correctors. We also investigate the problem of convergence rates for initial-boundary value problems.MSC2010: 35B27, 35K40.