Structure and dielectric properties of the group of Bi1.2+2yZn1.2-2yNb1.6O7+y (with y = 0-0.3) compositions have been studied. It was found that the cubic pyrochlore phase is predominant in these compositions under 1000 degreesC heat treatment. X-ray diffraction analysis and Raman spectra were used to investigate the crystal structure. Dielectric constant and dielectric loss of the samples were found to increase linearly with increasing of the y value for y less than or equal to 0.15. Structural defects such as porosity and second phase are responsible for the apparent deterioration of their dielectric properties for y > 0.15.