This paper discusses isoparametric technique for handling curvilinear geometries in high accuracy discontinuous Galerkin (DG) simulations for time-domain Maxwell's equations. With isoparametric elements, numerical fluxes along curved boundaries are computed much more accurately due to the high-order representation of the computational domain. Numerical experiments for 2D propagation problems demonstrate the applicability and benefits of the isoparametric technique for simulations involving curved domains.