We report the first electrochemically-based measurements of the rates of small polymer permeation into another polymer. The small polymer permeants are ferrocene ethylene oxide oligomers containing 2, 7, and 16 units and a propylene oxide oligomer containing 3 units. Their permeation into ultrathin microelectrode-supported films of the metal complex polymer poly[Ru(vbpy)(3)](ClO4)(2) was measured from acetonitrile solutions and from solutions in a methyl-endcapped ethylene oxide oligomer, MPEG-400 (MW = 400). Permeations of other ferrocenes with bulky substituents were also measured from acetonitrile solutions. In ah cases the permeability, PDPOL, into poly[Ru(vbpy)(3)](ClO4)(2) films is strongly dependent on the permeant molecular volume. Direct measurement of the partition coefficient, P, in acetonitrile shows that permeability variations among a series of related permeants are controlled more by variations in P than by diffusivity in the poly[Ru(vbpy)(3)](ClO4)(2) phase. Permeation of ferrocene polyether oligomers is much slower from MPEG-400 solutions than from acetonitrile; this appears to arise more from a decrease in D-POL than from one in P.