The morphology, mechanical and viscoelastic behavior of latex blends of unvulcanized natural rubber (NR) with carboxylated styrene-butadiene rubber (XSBR) were investigated, with special reference to the effect of the blend ratio, temperature, and frequency. Mechanical properties like tensile strength, modulus, and elongation at break were also studied. As the XSBR content increased, the tensile strength increased up to a 50:50 NR/XSBR ratio and then decreased as a result of the self-curing nature of XSBR. The dynamic mechanical properties of these latex blends were analyzed for loss tangent, storage modulus, and loss modulus. The entire blend yielded two glass-transition temperatures, which corresponded to the transitions of individual components, indicating that the system was immiscible. To determine the change in modulus with time, a master curve of 50:50 NR/XSBR blends was plotted. Time-temperature superposition and Cole-Cole analysis were done to understand the phase behavior of the latex blends. The experimental and theoretical values of storage modulus of blends were compared using the Kerner and Halpin-Tsai models. With the help of optical micrographs, attempts were made to correlate the morphology and viscoelastic behavior of these blends. (C) 2003 Wiley Periodicals, Inc.