Abstract: Rigid rodlike molecular chains-thermotropic liquid crystalline polymers (TLCP), which would self-organize into domains, showed anisotropy and excellent physical properties. In situ composites containing fibrils with high aspect ratios, high strength and high modulus as self-reinforcing components were prepared via incorporation of TLCP into thermoplastic polymers (TP), which led to significantly improve the processability due to the reduction in viscosity. A brief review on the rheology and microstructure of in situ composites was given, and factors influencing TLCP fibrillation and mechanical properties, such as chemical and physical properties of components including compatibility between TLCP and TP, as well as processing parameters were presented in this paper with the related work available in the literature. The state-of-the-art compatibility technology for TLCP/TP blends was elucidated in detail. A new concept of preparation of high performance in situ composites involving fibrils formed with the aid of application of an electric field during the processing was put forward for the first time.