Abstract: With sodium dodecyl sulfonate as phase transfer catalyst，N,N-dialkyl chitosan（N,N-DLCS-1 and N,N-DLCS-2）with different degree of substitution were prepared and characterized by FTIR，EA and 1H NMR. Properties of monolayers of these two samples were also studied. Experimental results showed that N,N-DLCS-1 has a higher degree of substitution，both samples could form a monolayer at the air-water interface. The sample N,N-DLCS-1 showed higher collapse pressure πc，maximum compressibility modulus Cs－1 and smaller extrapolated area Aex，the monolayer from which is more inseparable and stable due to the stronger intermolecular hydrophobic interaction derived from the higher degree of alkyl substitution.