Multiferroic materials which simultaneously exhibit electric polarization and magnetism have attracted more and more attention due to their novel physical properties and promising applications. Here, we report the magnetic and ferroelectric properties of single phase perovskite manganites Dy0.7Sr0.3MnO3 and Dy0.6Sr0.4MnO3 by varying temperature and magnetic field. Our results reveal that there exist spin reversal and strong antiferromagnetic pinning effects in both compounds, as well as negative magnetization in Dy0.6Sr0.4MnO3. Moreover, upon Sr-doping, spontaneous electric polarizations have been observed and the maximum polarization value of Dy0.7Sr0.3MnO3 is about 1000 lC/m2 while Dy0.6Sr0.4MnO3 reaches to 2000 lC/m2. The onset of the ferroelectric transition temperature is enhanced to be around 60 K. Our results indicate that the antiferromagnetic coupling is relevant to the ferroelectric properties of these fascinating multiferroic systems.