The polymerization of aminoethyl elaidamide in Langmuir and Langmuir-Blodgett films has been studied. In Langmuir films, changes induced by the polymerization process were investigated by pressure/area isotherm measurements and after transfer of the irradiated film by scanning force microscopy and IR spectroscopy. The pressure/area isotherms showed a phase transition at 16 mN/m, vanishing when the irradiation time is increased. At low resolution, scanning force microscopy images revealed that the irradiation induced the formation of structured domains. The shapes of these domains and the area occupied by these domains are dependent on irradiation time. At intermediate resolution, these domains which correspond to the polymeric phase appeared to be constituted of fibrillar structures characteristic of a crystalline polymer. Besides these domains, the film has a similar structure to the monomer film. For the polymerization in LB films, the changes in the structure of the film were followed by scanning force microscopy and LR spectroscopy as a function of irradiation time. Few changes in surface topography were observed at the micrometer scale during the polymerization. However we observed an increase of tip/sample interactions with irradiation time; moreover the irradiated film was found to be unsoluble. These results are indirect proofs of the polymerization.