Aged rats were divided into aged memory-impaired rats and normal aged rats based on their behaviour in the Moms water maze. Brain synaptosomal membrane fluidity and the effect of GM1 on it was evaluated by fluorescence polarization technique. The results showed that statistically significant decreases of the synaptosomal membrane fluidity in the neocortex and hippocampal formation were found in the aged memory-impaired rats compared with the young and normal aged rats, and that GM1 could ameliorate the abnormal membrane fluidity. Correlation analysis indicated that the brain synaptosomal membrane fluidity was closely related to aged learning and memory impairment. It was suggested that GM1 has a potential therapeutic value for aged memory impairment through altering neuronal membrane structure.