To study the pharmacokinetics of rhGH decorated by polyethylene glycol (PEG-rhGH) after sc administration in rat, serum PEG-rhGH concentrations were measured by 125I labeled method after sc in rat, the pharmacokinetic model and parameters were fitted and calculated by the 3P97 program. After sc injection at doses of 150, 300, and 600 microg x kg(-1) in rat, the serum PEG-rhGH concentration-time curves were fitted to a one-compartment model. The rhGH decorated by polyethylene glycol could prolong the action duration of rhGH in vivo, and reach the goal of long-action.