Ferrite compounds are very important materials due to their semiconducting and ferrimagnetic properties. Recently spinel ferrite ceramics have been found as perspective gas sensor materials with high sensitivity and selectivity to certain gases, as well as good long-term stability [1]. In the same time important spinel ferrite compounds are not still investigated as gas sensor materials. It is well known that such an application requires specific combination of physical, chemical, structural and surface properties [2] that could be achieved by choosing appropriate ferrite material and performed modification of its properties. Also there is limited information about the influence of heat treatment conditions (calcination temperature, heating and cooling rate) on structural properties such as chemical composition, stoichiometry, charge carrier concentration, cation substitution and distribution between ferrite sublattice tetrahedral and octahedral states and its dependence on gas sensing properties of spinel ferrite gas sensor materials. Mostly for improvement of ferrite material sensing properties researchers are trying to reduce ferrite particle, crystallite or pore sizes, as well as make specific structures (nanocubes, nanotubes, nanorods, nanobelts, and hierarchical structrures, as well as thin or thick sensing material layers) [3]. As a rule it is necessary to get nano-sized ferrite structures for materials used in gas sensor applications. For this reason several wet-chemical methods are adopted. The aim of the work was to study methods for charge carrier concentration control in spinel ferrites and to identify its influence on Ni-Zn ferrite gas sensitivity. Sol-gel auto combustion method was used for ferrite material synthesis [4]. Structural and microstructural characterization of synthesized ferrite materials was performed by means of X-Ray diffraction, chemical analysis and atomic force microscopy (AFM) methods. DC resistivity and its dependence from temperature, as well as gas sensitivity have been studied for various Ni1-xZnxFe2O4 ferrites obtained by using various heat treatment conditions.