Ordered molecular assemblies of novel alkylthio-substituted bis(naphthalocyaninato) rare earth complexes M[2,3-Nc(SC12H25)(8)](2) (M=Gd, Er) have been fabricated by Langmuir-Blodgett (LB) technique and characterized by surface pressure-area isotherm measurements, electronic absorption and polarized electronic absorption spectroscopy and low-angle X-ray diffractometry. The interaction between the thin films and NO2 gas was investigated. The experimental results indicate that the bis(naphthalocyaninato) rare earth molecules form well-ordered stable monolayers with face-to-face orientation for the macrocycles and edge-on configuration for the molecules at the air-water interface and lamellar multilayers on solid substrates. The orientation angles of naphthalocyanine rings with respect to the quartz plate surface in the LB films for M[2,3-Nc(SC12H25)(8)](2) with M of Gd and Er have been determined based on the polarized absorbance and found to be 50degrees and 54degrees, respectively. The adsorption-desorption process of NO2 on LB films of M[2,3-NC(SC12H25)(8)](2) has been monitored by electronic absorption spectroscopy. A process of gas desorption was found to obey the Elovich equation. (C) 2004 Elsevier B.V. All rights reserved.