Zeolite L type of high purity and high crystallinity was synthesized from mono cationic system. As L type has one-demensional channels parallel to the C-axis, the authors tried to cotrol the pore-opening size by coating with SiO_2 phase. L type was dipped into the solution prepared from the hydrolysis of TEOS or TMOS. L type coated was characterized by XRD, IR spectra and adsorption of gas. This coating method did not cause the changes of the basic zeolite structure. L type was coated with SiO_2 phase and new Si-O-Si bond was formed on the framework. L type coated with the solution prepared with TEOS:C_2H_5OH:H_2O:HCl = 1:2:1:1/50 adsorbed more amount of N_2 gas than L type with TEOS:C_2H_5OH:H_20:HCl = 1:2:2:1/50, in particular the internal adsorption of the former was larger than the latter. This suggested that as TEOS was hydrolyzed with the less amount of H_2O than the stoichiometric amount of hydrolysis (TEOS:H_2O = 1:2), the gel was constituted of the linear structure than of the three dimensional one. The compound of linear-like cluster was bound on the surface and around the pore opening. L type coated showed that the pore opening restrains the diffusion of C_6H_6 and N_2 molecules but allows to penetrate freely into the channel for H_2O molecules.