We report room temperature Brillouin light scattering measurements designed to probe the elastic properties of chemically ordered Co3Pt alloy films. A series of 100 nm thick films were deposited by molecular beam epitaxy at different growth temperatures (Tg) between 450 and 950 K. As the deposition temperature increases the lattice structure is observed to transform from a compositionally disordered, mixed fcc/hexagonal phase to a compositionally ordered, purely hexagonal phase, and finally to a compositionally disordered fcc phase. These structural transitions are accompanied by large changes in magnetic anisotropy, new features in the magneto-optical Kerr effect, and changes in the magnetic domain widths which all occur within about a 100 K temperature window centered around Tg=650 K. However, the independent elastic constants show no significant changes in the different films. These findings suggest that macroscopic strain effects are unlikely to underlie the diverse magnetic signatures observed within the chemically ordered phase. © 2002 American Institute of Physics.