Protein PEGylation (covalent attachment of poly(ethylene glycol) or PEG to proteins) is an excellent example of a drug delivery system, which improves pharmacokinetics and pharmacodynamic properties of therapeutics. A novel solid-phase PEGylation methodol. is presented herein, which involved conjugating protein to a cleavable heterobifunctional PEG deriv. tethered onto a solid matrix. The hydrolytic cleavage of the PEG chain from the solid matrix under mild conditions yielded PEGylated protein in the hydrolyzed fractions in free soln. A heterobifunctional PEG deriv. α-(β-alanine)-ω-carboxy PEG having mol. wts. 2000 and 4000 Da were prepd. inhouse and used for the surface-grafting and protein-conjugation. The amine terminal of this PEG deriv. was used for grafting onto carboxyl functionalized hydrophilic Sephadex derivs. The free PEG-carboxyl terminals were used for protein conjugation via amine coupling. Optimized PEG-grafting and hydrolysis conditions were developed for solid-phase protein PEGylation. Cytochrome c was used as a model protein and the presence of PEGylated species were confirmed in the hydrolyzed fractions using size exclusion chromatog.