Cellouronate is a (1,4)-β-D-glucuronan prepared by TEMPO-mediated oxidation from regenerated cellulose. We have previously isolated a cellouronate-degrading bacterial strain, Brevundimonas sp. SH203, that produces a cellouronate lyase (β-1,4-glucuronan lyase, CUL-I). In this study, the gene encoding CUL-I was cloned, and the recombinant enzyme was heterologously expressed in Escherichia coli. The predicted CUL-I protein is composed of 426 amino acid residues and includes a putative 21-amino acid signal peptide. The recombinant CUL-I specifically depolymerized β-1,4-glycoside linkages of cellouronate, and its mode of action was endo-type, like the native CUL-I. Sequence analysis showed CUL-I has no similarity to previously known polysaccharide lyases (PLs), indicating that CUL-I should be classified into a novel PL family.