Porous ceramics were produced by pressureless sintering green compacts composed of Si₃N₄ and TiN powders without additives in nitrogen gas atmosphere at 1700°C. The microstructure and electrical-properties of the Si₃N₄-TiN porous ceramics in a humid atmosphere were investigated. The following results were obtained: (1) The pore size distribution showed a sharp peak at 2000Å. (2) Rod-like shaped crystals of Si₃N₄ and equiaxed crystals of TiN distributed uniformly in the matrix. A large number of Si₃N₄ fibers of about 5μm were observed for 50wt% TiN. (3) The pore volume and specific surface area decreased proportionally with increasing amount of TiN. However, anomaly in the pore volume and specific surface area was observed at 50wt% TiN. (4) A sharp decrease in the impedance was observed in a dry atmosphere from 1×10⁷ to 1×10³Ω⋅cm for ceramics containing 40-60wt% TiN. (5) The impedance dependence of humidity was observed for ceramics in impedance higher than 10⁵Ω⋅cm (less than 40wt% TiN content). In a high humid atmosphere, the impedance decreased with increasing specific surface area.