A novel fiber-optic localized plasma resonance (FO-LPR) biosensor composed of a U-shaped optical fiber was proposed and demonstrated in the present study. The U-shaped optical fiber was fabricated by a femtosecond laser micromachining system. It was 105 μm in depth measured from the surface of the polymer jacket layer and 80 μm in width in the jacket layer. After treatment of annealing, the mean roughness of the surface was 342.24 nm as determined by AFM. The exposed surface of the U-shaped fiber was modified with self-assembled gold colloids to produce the FO-LPR sensor. Preliminary results show that the colloidal Au-modified U-shaped fiber by transmission power interrogation has a sensitivity of 1.768×10-3 RIU.