Materials which possess properties, which strongly suggest both ferroelectricity and ferrimagnetism, are found in the systems (Ba6−2xR2x) (Nb9−xFe1+x)O30 where R is a trivalent rare earth ion and x can vary from 0 to 1. X-ray diffraction powder patterns indicate a single phase having the potassium tungsten bronze type structure also exhibited by Ba6Nb8Zr2O30. When R is Gd+3 and x is at a maximum for this system, the material appears to be both ferroelectric and ferrimagnetic at room temperature. The ferrimagnetism is indicated by the appearance of a remnant polarization and the ferroelectricity by the presence of a dielectric hysteresis loop. The magnetic susceptibility is of the order of 120 at room temperature and exhibits dispersion at frequencies near 20 Mc. Other properties of materials in these systems will also be discussed.