The ability of a brown marine alga, Turbinaria conoides, to remove four rare-earth elements (REEs; lanthanum, cerium, europium, and ytterbium) was evaluated. Results showed that T. conoides was an excellent biosorbent for all four REEs. The equilibrium pH was found to severely affect the biosorption performance; pH 4.9 +/- 0.2 was found to be an optimum pH for favorable biosorption of REEs. The biosorption mechanism was found to proceed mainly by ion-exchange reactions between the lanthanide ions and the carboxyl groups present on the algal surface, confirmed by the pH edge, desorption, and scanning electron microscopy/energy-dispersive X-ray results. Biosorption isotherms were modeled using the Langmuir, Freundlich, and Toth isotherms, with the latter-described REE isotherms with very high correlation coefficients and lower error values. Maximum biosorption uptakes, according to the Langmuir model, were recorded as 154.7, 152.8, 138.2, and 121.2 mg/g for La, Ce, Eu, and Yb, respectively. Biosorption kinetics of REEs was found to be rapid, achieving 90% of total biosorption within 50 min. Desorption was successful with 0.05 M HCl, and the biomass was regenerated and reused for three sorption desorption cycles without a significant loss in the biosorption capacity.