  We present a photometric study of two new double-mode Cepheids, pulsating in
the first and second overtones modes: V470 Cas and GSC 2901-00089. For the
search of the double-mode variability, we used all available observations from
the ROTSE-I/NSVS and SuperWASP online public archives. Our multicolour CCD
observations in the B, V and R bands in Johnson's system confirm the double
periodicity of these variables. We study period variations of the two stars;
variations of the first overtone periods were reliably detected. In addition,
we consider the Petersen diagram for the Galactic 1O/2O Cepheids.
