We describe the lithographic properties of poly(N- isopentylmethacrylamide-co-t-butyl 4-vinylphenyl carbonate) [p(iPMA-tBVPC)] which has a structure that is subject to the main chain scission and to deprotection of t-butoxycarbonyloxy group by deep UV irradiation. The positive-tone patterns of the p(iPMA-tBVPC) LB film with 60 layers could be obtained by deep UV light irradiation, followed by development with alkaline aqueous solution. The resolution of the pattern was 0.75 μm, which is the resolution limit of the photomask employed. The photopattern formation with the copolymer [p(iPMA-tBVPC)] LB film was more sensitive than the homopolymer poly(N-isopentylmethacrylamide) [p(iP-MA)] LB film. The etching resistance of the p(iPMA-tBVPC) LB film deposited for the pattern of the gold film is also investigated.