The L-theanine was tested using confocal Raman microscopy. Obvious Raman bands were showed in the range of 250~1 700 and 2 800~3 000 cm-1. The Raman bands were assigned with a preliminary analysis and the characteristic vibrational modes were gained in different range of wave numbers. Eight strong Raman bands were observed in the Raman spectra at 321, 900, 938, 1 153, 1 312, 1 358, 1 454 and 1 647 cm-1, respectively. They are the characteristic Raman bands of L-theanine. The results showed that Raman spectroscopy might be a new kind of precise, direct and fast detecting method for theanine.