Structural characteristics and vibration spectra of pyridine and its donor-acceptor complexes with gallium halides were calculated by ab initio and density-functional methods. Complexes GaX₃Py are not rigid molecules with a flat potential-energy surface contour near the global maximum. Complex formation increases the negative charge on the pyridine nitrogen atom due to additional stabilization of the system by strengthened electrostatic interactions. The charge increase is provided by the rearrangement (distortion) of the pyridine structure, resulting in that most π charge is concentrated in the vicinity of the nitrogen atom. Standard thermodynamic characteristics of gas-phase dissociation of the complexes were calculated. Calculated ΔH^dis and ΔS^dis values quite well agree with experimental ones for the chloride adducts and strongly depart from them for the bromide systems. The short intramolecular X-H contacts suggest that the first stage of pyrolysis of the complexes involves elimination of hydrogen halide, while the gallium-nitrogen bond remains intact.