Abstract: AimTo establish a spectrophotometric method for measurement of the sizes of liposomes for evaluating physical stability of liposomes. MethodsThe sterically stabilized liposomes (SLs) were prepared by ethanol injection method and extrusion method. The mean cumulant diameters (D) of the vesicles were determined by electron microscopy and dynamic light scattering. On the basis of Rayleigh-Gans-Debye theory, the absorbance at 436 nm per unit lipid concentration (A_{436 nm}/C_p) was measured as a function of vesicle diameter. Resultslog(A_436nm/C_p) was closely related to logD (r²0.93, n=5). ConclusionThe absorbance of liposomes reflect their relative sizes and can be used to evaluate physical stability of liposomes.