This study aims to determine the adsorption potential of the cinnamon bark (CB), which is an agricultural waste, as an adsorbent for the removal of dyestuffs such as indigo carmine (IC) and malachite green (MG) from aqueous solution. Additionally, it includes the application of ?univariate and multivariate techniques? for determining the effects of key factors on adsorption process. The results obtained from experiments performed according to Central Composite Design (CCD) were evaluated with the Response Surface Methodology (RSM) approach. In optimum conditions (pH = 2, m = 1.80 g, t = 90 min, Co = 85 mg/L for IC and pH = 7, m = 0.45 g, Co = 30 mg/L for MG), the removal efficiencies of IC and MG adsorption onto CB were found as 84% ? 2 and 98.2% ? 0.2, with standard deviations (N = 3), respectively. The concordance of experimental data with pseudo-second-order kinetic model demonstrated that the adsorption was chemically controlled and an endothermic process that ongoing with increasing randomness on the adsorbent/adsorbate interface for both dyestuff removal. However, IC adsorption was non-spontaneous; MG adsorption was spontaneous. Because the equilibrium data were well explained to by Temkin isotherm model, the nature of adsorption was defined by the assumption that the binding energies of adsorption had a uniform distribution.