In situ measurement techniques suitable for determination of the coefficient of thermal expansion (CTE) in thin, spin-cast polymer films in both the in-plane and through-plane directions are presented. An examination of the thermal expansion behavior of cyclotene thin films has been performed. In particular, the effect of film thickness on the in-plane and through-plane CTE and in-plane Young＇s modulus of spin-coated cyclotene films was examined. It is shown that the mechanical response of in situ cyclotene films can be adequately described by isotropic film properties. It was also demonstrated that there is no thickness dependence on the free-standing mechanical properties or on the resulting through-plane thermal strain in an in situ film.