A chitosan/polypyrrole composited fiber as bio-compatible materials for artificial muscles is investigated. The chitosan/polypyrrole fiber (CPF) is fabricated by in-situ chemical polymerization of pyrrole monomer solution using FeCl3 as an oxidant. The electrical resistivity of the fiber is changed according to the strain variation applied to the both ends of the specimen. The sensor built by using the CPF has a higher gauge factor (4) compared to conventional metal strain gauges (~2) indicating a suitable material for delicate force control in sensing work.