A thin film made by the Langmuir-Blodgett technique from a polyamide precursor having at least 70% by mole of the recurring unit of the formula (1): ##STR39## wherein R1 is a tetravalent group having at least 2 carbon atoms, R2 is a bivalent group having at least 2 carbon atoms, and each of R3, R4, R5 and R6 is independently a hydrogen atom or a monovalent group having 1 to 30 carbon atoms selecte