The impact of polymer chain stiffness characterized by the bending modulus () on the glass transition temperature () of pure polymer systems, as well as polymer nanocomposites (PNCs), is investigated using molecular dynamics simulations. At small values, the pure polymer system and respective PNCs are in an amorphous state, whereas at large values, both systems are in a semicrystalline state with a glass transition at low temperature. For the pure polymer system, initially increases with and does not change obviously at large . However, the of PNCs shows interesting behaviors with the increasing volume fraction of nanoparticles () at different values. tends to increase with at small , whereas it becomes suppressed at large .