Terahertz (THz) communications are vulnerable to eavesdropping due to their scattering and diffraction properties, which limits their practical deployment. We propose a photonic THz chaos encryption and synchronization scheme to secure THz communications. We experimentally demonstrate the generation, encryption, and wireless transmission of a 5 Gbit∕s non-return-to-zero signal at 120 GHz using flexible photonic THz chaos. In addition, we achieve high-quality chaos synchronization with a neural network, attaining a correlation coefficient of up to 90.6%. This scheme offers a viable solution for secure THz communications, showing significant potential for enhancing wireless communication privacy.