In this paper we present the results of the studies on proton conduction in composites polyantimonic acid (PAA)-potassium dihydrophosphate (KDP) obtained by precipitation technique as well as mechanical mixing. The highest conductivity (~10-2 Sm/sm at 300 K) is achieved in the precipitated samples with volume fraction of KDP close to f = 13 %. The results of X-ray diffraction showed the absence of reflections from KDP for the samples with f < 20% and slight change in the intensities of odd and even reflections from PAA, which is explained by the ion exchange between the phases through the interface. These indicate that conduction is occurred through the interface regions of the composite. The value of interface conductivity is estimated from the dependence of the composite conductivity on the volume fraction of KDP based according to the model by Uvarov et al. This gives σs ≈ 5 Sm/sm, however the equation derived in this model doesn't represent the experimental data properly. Probably the maximum of the dependence simply corresponds to the percolation through the interface's continuous cluster – it is close to the classical percolation threshold.