The complex formation of an organized Langmuir-Blodgett (LB) film with transition metal ions in aqueous solutions was observed. The LB film of 5-(octadecyloxy)-2-(2-thiazolylazo)phenol (TARC18)) complexes with transition metal ions such as Ni(II), Cu(II), and Zn(II) in aqueous solutions, and the reaction was accelerated by photoillumination. The measurement of optical absorption spectra revealed that two kinds of complexes with the ligand to center metal ion ratios of stoichiometric 2:1 and 1:1 were formed in CuCl2 solution, while stoichiometric 1:1 complexes were formed in aqueous NiCl2 and ZnCl2 solutions. The X-ray diffraction and ESR measurements of the LB films confirmed that the regular arrangements of the LB films were retained even after the complex was formed with the metal ion. The optical absorption measurement and an inductively coupled plasma analysis of the metal ion complexed LB film showed that the LB film had a selective binding ability to Cu(II) ion when all the above metal ions were present in the solution.