Effects of cyanuric acid (CA) on the isothermal and nonisothermal crystallization, morphology, polymorphic crystalline structure, and phase transition on PBA have been investigated systematically by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared (FTIR) spectroscopy. The nonisothermal crystallization temperature increased upon addition of CA. The crystallization kinetics of isothermal crystallization was quantitatively analyzed. CA is an effective nucleating agent for the enhanced nucleation density and decreased spherulite size of PBA. Addition of CA was favorable for the formation of PBA alpha modification and accelerated the phase transition from the beta modification to the alpha modification. The mechanisms of nucleation, preferential formation of PBA alpha modification, and accelerated phase transition have also been proposed.