The optical properties of monocationic zeolite suspension adsorbed with each of Na^+, NH₄^+, Ca^(2+), and Al^(3+) were studied in the wavelength range 200∼800㎚. The results were as follows. 1. The optical density of zeolite suspension seemed to be affected by the light absorption of zeolite particles at the wavelength range of 200∼300㎚ and by the light scattering of zeolite particles at wavelength of 300∼800㎚. 2. At the wavelength range of 380∼800㎚, the optical densities of monocationic zeolites differed mutually according to adsorbed cations and increased in the order of Al- $gt; Ca- $gt; NH₄- $gt; Na-zeolite suspension. 3. It was convenient that at the wavelength range of 300∼800㎚, the diluted suspension of zeolite was measured in the short wavelength and the concentrated suspension of zeolite was measured in the long wavelength. 4. Zeolite particles in zeolite suspension were aggregated and the size of aggregation size was larger in the order of Al- $gt; Ca- $gt; Na $gt; NH₄- zeolite.