A new kind of amphiphilic polymer (poly(maleic acid) octadecanol "part" ester (PMAO)) with a larger ratio of carboxylic group to hydrocarbon chain was synthesized. In this report, this ratio between the carboxylic group and the hydrocarbon chain within a PMAO molecule is 2.0. This value is twice as large as that in common fatty acids. The LB films of the PMAO and its cadmium or lead salt possess an ordered structure, as determined by IR spectroscopy and X-ray diffraction measurements. The long spacing of the LB films of the cadmium or lead salt of PMAO is 5.7 nm. The hydrophilic part of a PMAO molecule was shown to form a nanometer-size aggregate. Therefore, when the LB films of the PMAO salts were reacted with H2S at lower pressure, PbS or CdS nanoparticulate multilayers were obtained. From the UV-vis spectra, it was found that the PbS as well as the CdS within PMAO LB films shows a larger blue shift of the optical absorption edge than that formed within the stearic acid LB films. This is due to the sulfide aggregation being restricted within one PMAO molecule. Moreover, the degree of polymerization and the ratio between the carboxylic group and the hydrocarbon chain can be changed. These structure characterizations of the PMAO molecule as well as its LB films imply that many kinds of inorganic nanoparticulate monolayers can be obtained, in which the size and the adjacent distance of the nanoparticles can be controlled.