We investigated effects of particle modification on physical properties of particle/liquid-crystal composites by polarizing optical microscopy and rheology. The surface modification of particles (ZrO2) was performed with an azobenzene carboxylic acid (8AB5COOH) in acetone. Surface coverage was evaluated as 56%. Under a polarizing microscope, the composites containing the surface-modified particle (8AB5COOH-ZrO2/8CB) exhibited characteristic textures in both smectic A (SmA) and nematic (N) phases. These textures could be observed repeatedly by changing the phase structures (SmA <----> N) indicating the presence of strong coupling between the particle surface and 8CB molecules. In the rheological measurements, we observed cooperative changes of steady shear viscosity associated with isotropic --> N phase transition in 8AB5COOH-ZrO2/8CB composites. With increasing the particle concentration, although the inherent discontinuous change of the viscosity around 42degreesG became small, a new characteristic change in the viscosity appeared around 46degreesC and became dominant. Effects of the shear rates on these changes suggest that structured regions may be formed with the modified particles. The viscosity change around 46degreesC would be attributable to the phase transition behavior of 8CB coupled with the particle surface in, the structured regions. In addition, the morphology of the system can be reversibly modutated with the aid of the isomerization of the azobenzene moieties.