We experimentally demonstrate the fabrication of silver/polydimethylsiloxane (PDMS) composite microline structures based on the simultaneous induction of the photoreduction of silver ions and the photopolymerization of PDMS using a femtosecond laser. We show that the fabricated line structures exhibit electrical conductivity and that the resistance of the structures increases when they are subjected to mechanical force. Demonstration of sensitivity to an external mechanical force obtained by exploiting flexible composite structures fabricated by a femtosecond laser is reported for the first time. The present technique using a femtosecond laser is promising for the fabrication of flexible optical/electrical devices.