It is found that beta glycine, the metastable polymorph of glycine, can be rapidly formed from gas phase via the sublimation of its stable alpha or gamma form in vacuum. The transformation process was monitored by infrared spectroscopy and the crystal structure of the sublimate was identified by X-ray diffraction techniques. It is the first report about the transformation of stable alpha or gamma glycine into metastable beta form in "one-step" (heating then cool down spontaneously). Crystallization of beta glycine from gas phase is very different from other methods that require additives in solution. The hydrogen-bonding interaction and self-assembling of amino acid were discussed based on the observations.