Detection of ammonia concentration in exhaled human breath is one of the early diagnoses of renal disease. A photonic crystal fiber (PCF) gas sensor is designed, which gives the highest relative sensitivity from the wavelength of 1.1 to 1.7  μm. The structure of the proposed PCF consists of five layers with elliptical holes rotated circularly around a core region. The core region consists of two layers with circular holes, which have a hexagonal layer and a central hole. The finite element method is used to investigate the optical properties of PCF. The results show that the proposed PCF gives the highest relative sensitivity of 81.05% at the wavelength of 1.544  μm, which is the absorption line of the ammonia gas. Other optical properties of the proposed PCF, such as confinement loss and effective area, are calculated at the wavelength of 1.544  μm, which equal to 0.31  dB  /  m and 8.71  μm², respectively. The impact of optical properties of the proposed PCF is investigated when the diameter of holes in the core and cladding region is changed. The results show that this structure shows good reliability for the manufacturing errors.