In this paper we investigate the origin of the dielectric relaxation characteristic of the nominally Bi1.5ZnNb1.5O7 (BZN) pyrochlore by a combined investigation of its electron diffraction and temperature-dependent micro-Raman spectra as well as its associated photoluminescence. It is found that the structural disorder and associated structural relaxation in BZN originates from short range chemical ordering of Bi/Zn in the A site of A(2)B(2)O(7) pyrochlores, which can make a contribution to the overall dielectric permittivity but does not necessitate its dielectric polarisation relaxation. The origin of dielectric polarisation relaxation in BZN is probably attributed to the oxygen vacancies as well as associated defect clusters. (C) 2011 Elsevier B.V. All rights reserved.