One of the main routes of peptide and protein delivery is parenteral. The need for daily or repetitive injection of these parenteral formulations is the main cause of patient non-compliance. The objective of this study was to prepare a controlled delivery system for peptide and proteins to increase patient compliance. Biodegradable triblock copolymers of PLGA and PEG (PLGA-PEG-PLGA) were synthesized and characterized using various content of glycolide. Solutions of PLGA-PEG-PLGA containing calcitonin as a model peptide were prepared and drug release from the sol-gel systems was evaluated in two different incubation conditions. Zero order release kinetics was achieved for up to 100 hours. No significant burst release effect was observed. It seemed that surface gelation was the main cause of drug release control. The release data fitted to Higuchi's modeling and showed good correlation. It can be concluded that in situ gelling system prepared in this study can be used for a weekly peptide delivery system.