The

DL

tryptophan (

DL

Trp) crystal was prepared by the mixed solventthermal method between neodymium carbonate and

L

tryptophan. The structure was characterized by FTIR

singlecrystal X-ray diffraction analyses. The results indicated that the cyrstallized

DL

Trp molecule possessed a centrosymmetric monoclinic space group P2(1)/c with a=1.89 08(2) nm

b=0.572 67(11) nm

c=0.930 32(15) nm and Z=4. It showed a threedimensional structure assembled by hydrogen bond of ′C-O-H-N′ interactions. The reasons for changing in configuration and the mechanism of the reaction were investigated by the curves of optical rotation and reaction time. The result indicated the transformation in configuration was a gradual change process. The temperature around 90 ℃ was important for configuration transforming of Trp.