The present invention provides a novel complex oxide capable of achieving high performance as a p-type thermoelectric material. The complex oxide comprises a layer-structured oxide represented by the formula Bi.sub.aPb.sub.bM.sup.1.sub.cCO.sub.dM.sup.2.sub.eO.sub.f wherein M.sup.1 is one or more elements selected from the group consisting of Na, K, Li, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Ca, Sr, Ba, Al, Y, and lanthanoids; M.sup.2 is one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Ni, Cu, Mo, W, Nb, Ta, and Ag; 1.8.ltoreq.a.ltoreq.2.5; 0.ltoreq.b.ltoreq.0.5; 1.8.ltoreq.c.ltoreq.2.5; 1.6.ltoreq.d.ltoreq.2.5; 0.ltoreq.e.ltoreq.0.5; and 8.ltoreq.f.ltoreq.10; and at least one interlayer component selected from the group consisting of F, Cl, Br, I, HgF.sub.2, HgCl.sub.2, HgBr.sub.2, HgI.sub.2, TlF.sub.3, TlCl.sub.3, TlBr.sub.3, TlI.sub.3, BiF.sub.3, BiCl.sub.3, BiBr.sub.3, BiI.sub.3, PbF.sub.2, PbCl.sub.2, PbBr.sub.2, and PbI.sub.2. The interlayer component being present between layers of the layer-structured oxide.