We first present the preparation of a new class of polyaniline (PANI)/titanium nitride (TiN) nanocomposites by in situ chemical polymerization in the presence of TiN nanoparticles. It was found that nanocrystalline TiN with an average diameter of similar to 20 nm incorporated and dispersed homogeneously within the polymer matrix, leading to enhanced conductivity and electrochemical activity. The interaction between nanocrystalline TiN and the polymer matrix was characterizd by XRD, FTIR, and UV-vis spectra. Interestingly, the morphology and structure of the PANI/TiN were controlled by the content of TiN nanoparticles in the composites. Structural changes are observed at TiN >= 30 wt %, where the in situ synthesis results in rod-shape composite particles. The electrical and electrochemical properties of the nanocomposites were also affected by the structure. The mechanisms of the property changes with the TiN contents are discussed. The structural difference was used to explain the different activation energies for the conductance process in emeraldine base (EB)/TiN composites.