Nafion (R) membranes were modified via in situ, catalyzed sol-gel reactions of titanium isopropoxide to form titania particles in the polar acid domains. FTIR spectroscopy showed successful intraparticle chemical bond formation with incomplete condensation of TiOH groups. Although such modification can lower membrane fuel cell performance, this study was aimed at reducing membrane degradation without significantly altering performance in the sense of material optimization. These incorporated particles did not change membrane equivalent weight and the water uptake was similar to that of the unmodified Nafion (R) membrane. Membrane dimensional stability, mechanical properties, and ability to withstand contractile stresses associated with humidity change at 80 degrees C and 100% RH were improved. An open circuit voltage (OCV) accelerated degradation test showed the titania modification held voltage better than the unmodified membrane. Performance deterioration of Nafion (R) after the OCV test was much higher than that of the modified membrane and the fluoride emission of the latter was lower. The degraded Nafion (R) membrane failed when subjected to creep, whereas the modified membrane remained intact with significantly low deformation. This inorganic modification offers a simple way to enhance membrane durability by reducing both physical and chemical degradation. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 2344-2353, 2011