The dependence of electrical conductivity of pyrochlore type Yb2+xTi2-xO7-x/2 materials shows that these materials are predominantly ionic conductors and are potential solid electrolytes for high temperature electrochemical applications. However, a detailed impedance study as a function of temperature revealed that a proper assessment of these materials must take into account significant effects of microstructure, composition and thermal history. At intermediate temperatures, the impedance spectra can be described by a series association of well separated contributions, and these could be ascribed to the properties of grain interiors, internal interfaces, and external electrode/material interfaces. The bulk and grain boundary properties were thus assessed and related to changes in microstructure and composition. The firing conditions also exert significant effects on the transport properties, especially for compositions which might deviate from the expected single phase range.