ZnSe-MgF2 thin films of different compositions were deposited by coevaporation on unheated substrates. Their optical properties were measured by spectrophotometry, their composition and density by Rutherford back scattering analysis, their structure by X-ray diffraction, and their residual stresses by interferometry. In the composition range under 60% of MgF2, the materials condensed well, and the thin films compositions were almost as deduced from the crystal rate controllers. The refractive indexes obtained vary from 1.7 to 2.6, following a Lorentz-Lorenz's law. The thin films are homogeneous and weakly absorbing (k equals 10-3) for wavelengths above 700 nm. The stresses are compressive for ZnSe, highly tensile for MgF2, and low compressive stresses were measured for compositions between 20 and 57% of MgF2. This behavior is correlated with a variation of the film structure from a polycrystalline to a quasi amorphous nature between 0 and 60% of MgF2. The residual stresses strongly depend on the film structure, while density and optical properties are statistical parameters that mainly depend on the ZnSe/MgF2 ratio.