Thermal sensitive polyurethane (TSPU) membranes were prepared by wet phase inversion technique，and used for selective separation of substances with different molecular sizes.According to differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis，it was found that the TSPU showed segmented structure and separate phase transition temperatures of soft segment phase and hard segment phase (the phase transition temperature of the soft segment phase was defined as the switch temperature，Ts).Polarizing optical microscope (POM) analysis showed that the soft segments of TSPU had a clear spherulite morphology at low temperatures (Ts).However，when the temperature exceeded Ts，the crystall of soft segments melted gradually and disappeared.The morphological structure of membranes was observed by scanning electron microscope (SEM) and atom force microscope (AFM)，the results indicated that the membrane showed relatively dense surfaces (or skin) and porous cross sections.The porosity of membranes measured by the mass loss of wet membranes after drying revealed that when the temperature increased from Ts-10℃ up to Ts+10℃，the porosity of membranes increased from 46.7% to 65.3%，showing a significant feature of thermal stimulation.When this TSPU membrane was used for separation of substances with different molecular sizes，we found that the ions of Na+ and Cl－(with small size) could permeate the TSPU membrane at any temperature，and higher temperature resulted in higher penetration rate.Whilst the penetration of glycin (with moderate molecular size) relied on the temperature variation.To be specified，at lower temperatures (T＜Ts)，the glycin permeation flux was very low，but when the temperature exceeded Ts，the permeation flux of glycin increased markedly，showing sensitivity to thermal stimuli.Collagen，due to its large molecular size，could not permeate the TSPU membrane in all temperature range.As a result，substances with different sizes could be selectively separated by the TSPU membrane under temperature controlling.