This paper presents the adsorption capacity of a biosorbent derived from the inner part of durian (Durio zibethinus) rinds, which are a low-cost and abundant agro-waste material. The durian rind sorbent has been successfully utilized to remove lanthanum (La) and yttrium (Y) ions from their binary aqueous solution. The effects of several adsorption parameters including contact time, pH, concentrations of La and Y, and temperature on the removal of La and Y ions were investigated. The adsorption isotherm and kinetics of the metal ions were also evaluated in detail. Both La and Y ions were efficiently adsorbed by the biosorbent with optimum adsorption capacity as high as 71 mg La and 35 mg Y per gram biosorbent, respectively. The simultaneous adsorption of La and Y ions follows Langmuir isotherm model, due to the favorable chelation and strong chemical interactions between the functional groups on the surface of the biosorbent and the metal ions. The addition of oxygen content after adsorption offers an interpretation that the rare-earth metal ions are chelated and incorporated most probably in the form of metal oxides. With such high adsorption capacity of La and Y ions, the durian rind sorbent could potentially be used to treat contaminated wastewater containing La and Y metal ions, as well as for separating and extracting rare-earth metal ions from crude minerals.