The role of liquid phase in the enhancement of the PTCR (positive temperature coefficient of resistance) effect in (Ba0.7Sr0.3)TiO3 (BST) with the addition of AST (4Al(2)O(3).9SiO(2)-3TiO(2)) is investigated in this paper. The AST-BST samples were characterized with optical microscopy, transmission electron microscopy, energy-dispersive spectroscopy, and impedance spectroscopy. Microscopic observations showed that slower cooling might facilitate the precipitation of the (Ba,Sr)TiO3 phase from the liquid phase on matrix grains since the amount of liquid phase was reduced with a decreasing cooling rate. Impedance spectroscopy indicated that this variation accompanied the change in the intrinsic properties of grain boundaries, which could not be explained by well-known oxidation effects. With the aid of a brick-layer model and high-resolution transmission electron microscopy (HRTEM), it appeared that the change in electrical characteristics of grain boundaries with decreasing cooling rate originated from the precipitation of (Ba,Sr)TiO3. Finally, the effect of precipitated (Ba,Sr)TiO3 on the PTCR characteristics is discussed in terms of the acceptor-state density and the polarization state at grain boundaries.