In order to investigate the microstructure dependence of the monoclinic-triclinic phase transition of Bi26Mo9WO69, dense samples with different grain sizes were produced by isostatic pressing and controlling sintering temperature and time. The structural and electrical properties were studied by X-ray diffraction (at room and at high temperature) and impedance spectroscopy, respectively. The influence of the microstructural properties on the triclinic-monoclinic phase transition and on the electrical properties of the Bi26Mo9WO69 were described by the following parameters derived from the fitting of impedance diagrams: depression angle, relaxation frequency and total electrical conductivity. Impedance spectroscopy results are in agreement with the high-temperature X-ray diffraction data; both techniques show that phase transition kinetics depends on the microstructural properties, remarkably on the grain size.