In present work, hollow silica spheres (HSS)/Nafion (R) composite membranes were prepared by solution casting. The thermal properties, water retention, swelling behavior and proton conductivity of the composite membranes were explored. It was found that HSS dispersed well at micrometer scale in the obtained composite membranes by SEM and TEM observation. Thermal properties of composite membranes were improved than that of recast Nafion (R) membrane. Compared with the recast Nafion (R) membrane, the composite membranes showed higher water uptake and lower swelling degree at the temperature range from 40 to 100 degrees C. At the same HSS loading, the smaller the diameter of HSS in composite membranes, the more the water uptake, however, the swelling degree of composite membranes was increased. The proton conductivity of the composite membrane with 3-5 wt.% HSS (120 and 250 nm) increased distinctively at above 60 degrees C, reached the optimal value at 100 degrees C, and decreased slowly when the temperature exceeded 100 degrees C. (C) 2008 Elsevier B.V. All rights reserved.