Copolymers of poly(ethylene oxide) (PEO) and 5,5'-azodisalicylic acid (Olsalazine, OLZ) were synthesized and evaluated by hydrolysis and in-vitro biodegradation with azoreductase. It was found that changing the molecular weight of the PEO blocks affected the loading ratio of OLZ, and resulted in significant differences in the hydration and degradability of the copolymers. These novel azo-containing copolymers can be used in colon-specific drug delivery.