We design a simple photonic crystal fiber-based refractive index biosensor (PCF-RIBS) and analyze its sensing performances using the finite element method. We analyze the loss spectra of PCF-RIBS for a wide range of wavelengths from visible to near infrared (0.4–2 μm). Besides, we extend the sensing performances in terms of loss spectra for three sets of refractive indices of analyte, na. From the detailed study, we find that the PCF-RIBS exhibits a highest spectral sensitivity of 12,000 nm/RIU with a corresponding resolution of 8.33 × 10−6 RIU and amplitude sensitivity of 11,412 RIU−1 with a resolution of 8.76 × 10−8 RIU when the refractive index is varied from 1.44 to 1.45. Finally, we also examine the robustness of the proposed sensor by perturbing some of the structural parameters, namely, thickness of the metal layer and diameter of the air-holes. © 2018