A composition which includes oxyntomodulin and polyethylene glycol polymer (PEG polymer) linked via a reversible linker such as 9-fluorenylmethoxycarbonyl (Fmoc) or 2-sulfo-9-fluorenylmethoxycarbonyl (FMS) is disclosed. Pharmaceutical compositions comprising the reverse pegylated oxyntomodulin and methods of using same are also disclosed.