It is an object of the invention provides a method of manufacturing a tea beverage having an excellent aroma. The invention provides a method of manufacturing a tea beverage, which comprises the steps of preparing an extract of tea leaves containing 40 ppm-210 ppm of theanine, bringing the extract of tea leaves thus prepared into an anaerobic condition, heat-treating the extract of tea leaves in the state of anaerobic condition at a temperature of not lower than 100.degree. C. under tightly sealed, and filling the extract of tea leaves thus heat-treated into a hermetically sealed container.