Nonlinear optical films were vapor deposited onto Si(100) and indium‐tin‐oxide‐coated glass. These films are guest‐host‐type polymer and showed electrooptical (EO) properties after poling. The host polymer is Teflon AF 1600 (AF) and the guest is dimethylaminonitrostilbene (DANS). Deposition is done by coevaporation. EO effects were found in films containing 5–25 vol % DANS. The EO coefficientr33, is found to be a function of composition, poling temperature, and cooling rate during poling. The highest EO coefficient obtained is 2.4 pm/V from a film with 10 vol % DANS and poled at a temperature of 130 °C. Very little or no EO effects were found for films with ≳25 vol % DANS. This is found to be a result of phase separation and subsequent crystallization of DANS. A decrease of EO effect at higher poling temperature is possibly a result of thermal disorder which was ‘‘frozen’’ during cooling. DANS was also found to react with Teflon AF 1600 at a higher DANS concentration. ©1995 American Institute of Physics.