Abstract. [Cd(C3H6NOz)2].3H20 , M r --342.6, trigonal, P3121, a = 6.376 (3), c = 25.59 (2)/~, V= 901 (1) ,&3, Z=3, Dx=l.86(4)gcm -3, MoKa, 2=0.7107,/t, /1 = 18.4 cm -1, F(000) = 516, T= 298 K, R = 0.031, wR = 0.040 (w = 1) for 1109 independent reflexions. The metal coordination is octahedral; two alanine molecules are coordinated to the Cd atom as a bidentate ligand with a cis-O,O-trans-N,N donor set while the other two coordination positions are occupied by oxygen atoms of water molecules. The amino groups, carboxylic groups and the waters of coordination are fully hydrogen bonded to form sheets parallel to the (001) plane. These sheets are hydrogen bonded by the other water molecule.