Three new derivatives of vitamin B, ?. 0"-succinyl-, 05'-s~~cinyl-, and 02'. 0"-disuccinyl-vitamin B, 1. whose a-ribose moieties of the nucleotide ligand are succinylated, were prepared by reaction of the vitamin with succinic anhydride. The first succinylstion took place rapidly and almost predominantly on 5'_OH of a-ribose, and the second succinylation much more slowly on Z'-OH. From the behaviors in paper electrophoresis and the lability to CN-of cobalt-base bond of OZ.-succinylated vitamin B, 2 derivatives, it was suggested that the terminal COOH of the 02' -succinyl group forms an inner salt with the imidazole nucleus of .5.6-dimethylbenzimidnzole. hlonosuccinyland disuccinyl-vitamin B, 2 were easily reconverted into vitamin B, 2 by mild acid or base hydrolysis. Huting at 130" for 5 min also led to the complete severance of the succinyt group of OS'succinyl-vitamin B, =_ None of the three succinyl derivatives inhibited the diol dehydrase reaction when added wjth coenzyme B, 2, suggesting that the ability to bind to the apoenzyme is strongly diminished or almost lost by succinylation on 2'-or S'-OH of r*-ribose. None of the succinyl vitamin B, 2 compounds showed either biological activity or anti-vitamin B, = activity when tested wirh EscJzen'chti coli 215, a methionine-B, 1 nuxotroph. None of them significantly inhibited ['HIvitamin B,, uptake by E. coli 215 cells. Thii observation implies that succinyl derivatives of vitamin B, z are hardly incorporated into the cells of E. COIL