Dielectric anisotropy of polymers with low dielectric constant is an important property to consider for developing interlevel dielectrics for advanced on-chip interconnects. The effect of molecular structure on dielectric anisotropy has been Investigated for two low dielectric-constant polymers: a fluorinated polyimide, FPI-136M and a fluorinated poly(aryl ether), FLARE-1.51, Optical and electrical measurements have been carried out to determine the dielectric anisotropy in blanket thin films and trench line structures. Results from optical measurements show that the FPI-136M film has a larger birefringence than the FLARE-1.51 film, indicating a larger dielectric anisotropy; This reflects a higher degree of in-plane molecular orientation for the rigid rod-like: fluorinated, polyimide, while the fluorinated poly(aryl ether) has an ether linkage that allows greater chain flexibility. Electrical measurement of the dielectric anisotropy has been performed using a metal-insulator-metal structure to determine the out-of-plane dielectric constant and an interdigitated submicron metal line structure coupled with a two-dimension computer model to determine the in-plane dielectric constant. Results show that the rigid rod-like FPI-136M has a smaller dielectric anisotropy compared with that measured from the optical birefringence. In contrast, the dielectric anisotropy of the more flexible FLARE-151 is found to be similar to that obtained from the optical birefringence measurement. Fourier transform infrared (FTIR) spectroscopy has been used to examine the molecular structures in the blanket films and the trench line structures. The FTIR spectra of FPI-136M show that its molecular structure in submicron trenches is significantly different to that in spin-coated blanket film. This is in contrast to FLARE-1.51, which has similar molecular orientation for the blanket film and the trench structure. Thus, the molecular orientation of the rigid rod-like FPI-136M seems to be more affected by the confinement in submicron trenches, giving rise to a lesser degree of dielectric anisotropy than that observed in blanket films.