Double molybdates, KLn(MoO4)2 and K5Ln(MoO4)4 have been synthesised utilising the solid state reactions of KIO3 Ln203 and MoO3 (Ln=La,Gd,Dy) in appropriate mole ratios, employing thermal analysis techniques. The solid phases have been characterised by IR, XRD studies and magnetic measurements. The d.c. electrical conductivity values of the two molybdates measured in the temperature range 373–623K are found to increase with rise in temperature. This observation together with the calculated jump activation enthalpies and the supposed ‘layered’ type structure with the loosely held K+ ion between the layers support the ionic conductivity mechanism in these samples.