The self-assembly between poly(4-diazonium styrene)(PDS) and poly(sodiumsulfonate styrene)(PSS) was investigated．The mutilayer ultra thin films were fabricated layer-by-layer successfully from PDS and PSS．After heating for 10 min at 70℃ the multilayer film became very stable towards polar solvents．No considerable changes were observed for the heated film soaked in DMF (20℃) for 48 h

while the unheated film almost destroyed at same condition．The dramatic improvement in stability of the film towards polar solvents should be attributed to the conversion of bonds between the layers of the film from ionic bond to covalent bond under heating．