An adsorption equilibrium apparatus (gravimetric method) was used to obtain the water vapor isotherms on zeolite 3A, potato starch, corn starch, cassava starch, and cellulose at room temperature. Experimental results show that at low relative pressure, P/P(0) = 0.6, the water-ethanol sorption ratio in potato starch was the highest at 64.2. The obtained sorption ratios from high to low are potato starch, cellulose, corn starch, cassava starch, and zeolite 3A. It was found that starch biosorbents are a better choice than zeolite 3A for the selective adsorption of water and ethanol. Several isotherm models Langmuir, modified Brunauer-Emmett-Teller (mod-BET), Halsey, Smith, Henderson, Oswin, Ferro-Fintan, Guggenheium-Anderson-De Boer (GAB), or Peleg-were applied to fit the water and ethanol vapor equilibrium data obtained from this study. The accuracy of the models was evaluated by using the average relative deviation. The Langmuir model was better for the zeolite 3A adsorption system. The starch biosorbent isotherms were fitted well using the GAB, Ferro-Fintan, or Peleg models. The Peleg model with four parameters gave the best fit for the starch system, and the Smith model was good for the cellulose system.