A process for enhancing theanine extraction from plant material through a series of extraction, adsorption and filtration steps. More specifically, disclosed is a process for isolating theanine from a plant material, which includes the steps of: a) contacting the plant material with a solvent to obtain an extract comprising theanine; b) contacting the theanine extract with an adsorbent to obtain a theanine-containing eluate; and c) subjecting the theanine eluate to a filtration step to obtain a theanine-rich extract.