Symmetric (homogeneous) and asymmetric membranes (non-homogeneous) made of poly(phenylene oxide) (PPO) and symmetric membranes made of polyamide (PA) were studied by electron spin resonance (ESR), using the nitroxide spin as a probe, and by Raman scattering. These studies indicated that the morphology of the polymer chains in the asymmetric membrane was slightly different than in the symmetric membrane. This difference may be due to the different morphology of the polymer chain in the dense layer (top layer) of the asymmetric membrane. Raman scattering of PA membranes could not be observed due to the high intensity of the fluorescence. From the ESR study of PA membranes it was noticed that there was no significant decaying effect on the membranes due to time and air (atmosphere) for a long period.