The potential of water hyacinth ash for phenol adsorption from aqueous solution was studied. Batch kinetic and isotherm studies were carried out under varying experimental conditions of contact time, pH, phenol concentration, and solution temperature. The adsorption of phenol was studied at pH 7. Batch adsorption models, based on the assumption of the pseudo-first-order, pseudo-second-order, and Elovich models, were applied to examine the kinetics of the adsorption. The results showed that kinetic data followed closely to the Elovich kinetic model. The experimental data were further analyzed by the expression of Boyd and the intraparticle diffusion model to determine the actual rate controlling steps. The overall rate of phenol uptake was found to be controlled by external mass transfer at the beginning of adsorption; then it gradually changed to intraparticle diffusion control at a later stage. Various adsorption models were used for the mathematical description of adsorption equilibrium and it was found that the experimental data fitted very well to the Langmuir model. Different thermodynamic parameters such as free energy, enthalpy, and entropy have been calculated and it was concluded that with the increase in temperature adsorption decreases, indicating the exothermic nature of the process.