A low cost and environmentally friendly adsorbent was developed based on leaf of platanus sp. to adsorb cadmium ion in water. The adsorbent was modified with citric acid and then also encapsulated in agar for easy separation after the adsorption process. Parameters such as adsorbent dose, stirring time, solution pH and modification of the adsorbent with citric acid were investigated in a batch experiment in order to determine the optimum condition for Cd (II) adsorption. Based on the Langmuir isotherm adsorption model, the adsorption capacity of cadmium ion for raw adsorbent, modified adsorbent with citric acid and encapsulated adsorbent were 3.69, 15.31 and 6.89 mg/g, respectively. The high adsorption capacity after treatment with citric acid may be due to the increase in carboxylic content of the adsorbent surface and also the increase of surface area and pore volume of the adsorbent. With this high adsorption capacity for cadmium ion and an abundance of raw materials, this bio-adsorbent could be considered as a low cost adsorbent in the near future.