Grain structure of porous sodium niobate ceramics (with 3-0 connection and variable porosity changing from 1.0 to 13.6%) fabricated under different conditions is investigated and the microstructure parameters are calculated for different degrees of porosity. It is demonstrated that with increasing degree of porosity, the character of the sodium niobate grain structure changes due to the formation and ordering of the pore - multilayered grain coating clusters, sharp increase in the total pore surface area, and its significant excess over the external sample surface area. These structural changes can influence significantly the integral electrophysical characteristics of the porous sodium niobate ceramics and determine a high degree of its piezoanisotropy. Since the discovery of segnetoelectricity in BaTiO3, the material science direction of physics of materials with special electric properties (segnetoelectric (SE), antisegnetoelectric (АSE), and piezoelectric materials) aimed at expansion of their application field and fulfillment of more stringent requirements to their operational characteristics has been developed in two independent ways by means of complication of 1) their chemical (element and component) structure of composites and 2) their phase state (relative contributions of electrically active and passive components). The first case involves transition from a single-component compound (ВaTiO3) to n-component (n = 2-6) systems most often based on PbTiO3 and PbZrO3 (the so-called PZT structures) with morphotropic boundaries and extreme properties of solid solutions. The second case involves manufacture of composites with variable connection of their phases, including porous ceramics whose pores play the role of a nonpiezoactive medium. The porous ceramics has been investigated in detail from the viewpoint of its technical application (1-8), but has poorly been understood as a physical object. In the literature, segnetoelectrics manufactured from porous ceramics with 3-3 connection (with open porosity when pores connected with each other form channels emerging onto the surface) are mostly described. The porous ceramics of this type is conventionally fabricated through significant complication of the production process by means of introduction of additional operations with organic porophores. However, data on АSE porous ceramics with various connection types, including 3-0 connection (closed isolated porosity caused by small changes of the production process), are lacking. Taking into account a significant dependence of the properties (first of all, electrophysical) of materials based on niobate of an alkali metal on their microstructure (porosity and grain structure), the present work is aimed at detailed investigations into the grain structure and microstructure parameters of polycrystalline sodium niobate (SN) NaNbO3 with closed porosity type (3-0 connection).