A series of polyurethaneurea-vinyl polymer (PUA) hybrid aqueous dispersions were synthesized from castor oil and/or difunctional poly(oxypropylene) polyol (GE-210, M-n = 1000), butyl acrylate, and styrene. The effect of hybrid between the polyurethaneurea (PUU) and vinyl polymer (PA) on the morphologies and the mechanical properties for these PUA films was examined and studied. The experimental results showed that there was appreciable miscibility between the PUU and PA phases for the PUA prepared with GE-210, giving rise to less ordered hard segments in PUU and resulting in lowering of some mechanical properties compared with those of pure PUU synthesized with GE-210. For PUA based on castor oil, the compatibility between the PUU and PA phases was also observed, although there was a network structure in the system. Moreover, the particle-accumulation morphology during the film formation process for this PUA system disappeared, but this behavior was found for a similar PUU. In this case, a great improvement of mechanical properties for such a PUA specimen was observed. The other PUA specimens with high content of castor oil exhibit excellent comprehensive mechanical properties, resulting from the reinforcement of cross-linked PUU phase existing in the systems.