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Solid solutions of the structure γ-K4P2O7, which have the composition (K1 – xRb x )3.8M0.1P2O7(M = Ca, Sr, Cd, Ba) and (K1 – xRb x )4 – 2yCa y P2O7(y= 0.025–0.20), are synthesized. The solutions' electroconductivity is studied in the temperature range 400–600°C. The concentration dependences of the conductivity and the activation energy for conduction have extremums at x≈ 0.6, which points to the polyalkaline effect. The effect increases with decreasing radius of cation M2+and with increasing concentration of calcium cations, which is explained by an increased energy nonequivalence of positions in the cation sublattice accessible to alkali ions.