AbstractSurface activity of aqueous solutions of cellulose acetate (CA) with total degree of substitution (〈F〉) ranging from 0.58 to 0.80 was examined. Critical micelle concentration (CMC) of the aqueous CA solutions, determined from the polymer concentration dependence of surface tension (γ), is unequivocally determined by 〈F〉, and an increase in 〈F〉 of CA brings about a lowering of the CMC. From light scattering measurements on aqueous solutions of CA with 〈F〉 = 0.8 at 20°C, it was revealed that in the vicinity of the CMC the micelles in the solution consist ofc. four CA molecules, which is very close to the value obtained by analysing the data obtained from the mass action model. The surface tension of aqueous solutions of CA (〈F〉 = 0.8) in the polymer concentration range above the CMC wasc.0.74 times that of pure water over the tem