A study was conducted to demonstrate lasing action by composite electrospun polymer nanofibers emitting in the visible and near-infrared (NIR) spectral region. It also demonstrated the significant potential of electrospun and flexible gain nanofibers as active waveguides and lasers. Single-mode optically pumped lasing sources on individual electrospun nanofibers emitting at 585 nm with linewidth 0.3 nm and excitation threshold fluence of 60 μJ cm -2 were demonstrated as a prototype system. The single fiber surface was found to exhibit a root-mean-square roughness of about 6 nm using atomic force microscopy (AFM). The fibers were tested for laser emission and it was revealed that each fiber constituted a Fabry-Pérot cavity for spectral selection and light amplification, due to the high confinement of the emitted light.