We study interfacial properties of poly(n-hexyl isocyanate) (PHIC) films by surface pressure and interfacial pressure measurements and fluorescence microscopy as a function of the molecular weight of PHIC. The respective surface pressure-area isotherms exhibit a plateau indicative of multilayer formation, the plateau region is narrower, and the plateau surface pressure is higher with an increase in the PHIC molecular weight. PHIC having a contour length less than the persistence length behaves as a rodlike polymer at the air-water, and with an increase in the molecular weight the PHIC chains undergo chain entanglements to give smaller extrapolated area. Such a molecular weight dependence is in good agreement with the fluorescence images at the air-water interface. At the oil-water interface PHIC forms a monolayer and the interfacial pressure is constant below the area of 0.28 nm(2)/monomer unit of PHIC. The area is in good agreement with an area calculated by assuming that a rodlike cylindrical PHIC molecule lies on the water, irrespective of the molecular weight of PHIC.