The current invention provides methods (e.g., large-scale processes) for the production of nucleotide sugars, which are modified with a polymeric modifying group, such as poly(alkylene oxide) moieties (e.g., poly(ethylene glycol) or poly(propylene glycol)) moieties. A typical process of the invention includes anion exchange chromatography followed by an ultrafiltration procedure, such as tangential flow filtration. The process of the invention provides modified nucleotide sugars in unexpectedly high purity and high overall yields.