A highly sensitive hexagonal lattice refractive index (RI) sensor based on photonic crystal fiber (PCF) is presented and analysed in this paper. The sensing performance of the presented sensor is analysed using the finite element method (FEM) in the presence of perfect match layer (PML) and scattering boundary conditions. From the simulation, it is shown that the highest wavelength and amplitude sensitivity of the suggested sensor reaches to 19,000 nm/RIU and 910 RIU −1 , respectively for both x- and y-polarized modes due to the analyte RI variation from 1.36 to 1.40. Additionally, the highest RI resolution of 5.26×10 −6 RIU and an excellent value of coefficient of determination (R 2 = 0.9977) are gained for this proposed sensor. Therefore, because of having the good sensing performance the proposed sensor can be a promising device for biomolecules and chemicals detection.