A cross-linkable amphiphilic copolymer of N-dodecylacrylamide with N-(11-acryloylundecyl)-4-vinylpyridinium bromide was prepared. This polymer when spread on a water surface forms a stable condensed monolayer that was transferred onto a solid support to yield a Langmuir-Blodgett (LB) film. On UV light irradiation, the polymer LB film became insoluble in all organic solvents because of the formation of a two-dimensional photo-cross-linked polymer network. The cross-linking reaction was found to be caused by dimerization of acryloyl groups in the LB film. Fine negative resist patterns based on the insoluble two-dimensional polymer network can be drawn clearly after development of irradiated LB films with a solvent. The patterns of the cross-linked polymer LB films of various film thicknesses from bilayer to 200 layers were successfully achieved by using a conventional photolithographic technique. The bilayer patterns of cross-linked polymer LB films were observed using atomic force microscopy (AFM). These films had a thickness of 1.0 nm and a uniform surface.