Ferroelectricity in type-II multiferroics is induced by breaking of inversion symmetry by certain type of spin structure below the magnetic ordering temperature. Therefore, a knowledge of spin structure is imperative to find new magnetoelectric multiferroic materials. In RMnO3 (R=Dy and Tb), the interaction between Dy and Mn enhances the ferroelectric polarization arising from cycloidal spin structure of Mn-ions due to induced ordering of Dy-ions by Mn-ordering. In Gd0.5Dy0.5MnO3 system, our magnetoelectric measurement suggest that the Mn-polarization is suppressed at the R-ion ordering temperature. On the other hand, the low temperature ordering of R-ion itself induces independent electric polarization. Therefore, it is important to understand the magnetic structure of R-ion and Mn-ion at low temperatures.