The effects of n-alkanols on the rotational relaxation time of 1,6-diphenyl-1,3,5-hexatriene (DPH) were investigated in the liposomes of total lipids (SPMVTL) extracted from synaptosomal plasma membrane vesicles. n-Alkanols decreased the rotational relaxation time of DPH in the SPMVTL, and the potencies of n-alkanols up to 1-nonanol increased by 1 order of magnitude as the carbon chain length increased by two carbon atoms. The cut-off phenomenon was reached at 1-decanol, where further increase in hydrocarbon length resulted in an increase in the rotational relaxation time of DPH.