Percolative properties in dielectric (DE) tunability were observed in three ferroelectric (FE)-DE composite ceramics as follows: xBa0.5Sr0.5TiO3–MgO, xBa0.4Sr0.6TiO3–Mg2TiO4, and xBa0.5Sr0.5TiO3–Mg3B2O6. Dielectric constants of the composites increased monotonously with increasing volume fractions of FE component. Comparatively, their DE tunabilities exhibited a weak dependence on FE concentrations over a wide range. However, their tunabilities started to decrease substantially below a critical concentration of FE. The critical concentrations were 40 vol % for Ba0.5Sr0.5TiO3–MgO, 38 vol % for Ba0.4Sr0.6TiO3–Mg2TiO4, and 33 vol % for Ba0.5Sr0.5TiO3–Mg3B2O6. These results could be used as a guide to tailor the properties of FE-DE composites for tunable device applications.