K 0.5 La 0.5 Bi 2 Nb 2 O 9 , a relaxor, was synthesized and the structural studies confirmed it to be an n=2 member of the Aurivillius oxides. The 12{h00} and 12{hk0} types of superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein Ea=0.04eV, Tf=428K,and ωo=1010Hz. The diffuseness parameter γ=2.003 established the relaxor nature and it was attributed to the A-site cationic disorder. The piezoelectric d31 coefficient was 0.5pC∕N at 300K and 2pC∕N at 480K.