Whole genome sequence from Acinetobacter baumannii isolate Ab-46-1632 reveals a novel KL144 capsular polysaccharide (CPS) biosynthesis gene cluster, which carries genes for D-glucuronic acid (D-GlcA) and L-rhamnose (L-Rha) synthesis. The CPS was extracted from Ab-46-1632 and studied by 1H and 13C NMR spectroscopy, including a two-dimensional 1H,13C HMBC experiment and Smith degradation. The CPS was found to have a hexasaccharide repeat unit composed of four L-Rhap residues and one residue each of D-GlcpA and N-acetyl-D-glucosamine (D-GlcpNAc) consistent with sugar synthesis genes present in KL144. The K144 CPS structure was established and found to be related to those of A. baumannii K55, K74, K85, and K86. A comparison of the corresponding gene clusters to KL144 revealed a number of shared glycosyltransferase genes correlating to shared glycosidic linkages in the structures. One from the enzymes, encoded by only KL144 and KL86, is proposed to be a novel multifunctional rhamnosyltransfaerase likely responsible for synthesis of a shared α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → 3)-L-Rhap trisaccharide fragment in the K144 and K86 structures.