We report a successful approach for the fabrication and characterization of a fiber-optic sensor for ascorbic acid (AA) detection, using a molecularly imprinted polyaniline-Ag (PANI-Ag) nanocomposite layer based on the combined phenomena of surface plasmon resonance (SPR) and localized SPR (LSPR). The PANI-Ag nanocomposite is synthesized by an in situ polymerization process and AA imprints are prepared on the polymeric composite. The confirmation of the PANI-Ag nanocomposite and AA imprinting is performed using various characterization methods such as x-ray diffraction (XRD), UV-vis, Fourier transform infrared spectroscopy and scanning electron microscopy. From XRD, the size of Ag nanoparticles is analyzed. The absorbance spectra are recorded for samples of different concentrations of AA around the sensing region of the probe. An increase in peak absorbance wavelength with the increase in AA concentration is observed with a linear response for the concentration range from 10(-8) M to 10(-6) M. The sensor possesses a high sensitivity of 45.1 nm log(-1) M near an AA concentration of 10(-8) M. The limit of detection (LOD) and limit of quantification of the sensor are found to be 7.383 × 10(-11) M and 4.16 × 10(-10) M, respectively. The LOD of the sensor is compared to studies reported in the literature and is found to be the lowest. The sensor possesses several other advantages such as cost effectiveness, selectivity, and low response time (<5 s), along with abilities of remote sensing and online monitoring.