Iron sulphide nanocrystalline (FeS NCs) may have significant potential for applications in many areas. Ultrasonic spray pyrolysis (USP) method is used to deposit mackinawite FeS NCs film on glass substrate at 335 degrees C in this study. The film was characterized by vibrational (FTIR and Raman) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis spectra. The observed diffraction peaks at 2 theta angles 28.12 degrees and 50.45 degrees correspond to the lattice planes (103) and (112) respectively. The crystallite size was calculated to be around 10 nm by using the Scherrer equation with the peak corresponding to the (112) plane. Raman spectrum revealed four peaks placed in the region of 200-750 cm(-1) due to mackinawite FeS phase. FTIR spectrum revealed two peaks at 649 cm(-1) and 827 cm(-1) that are attributed to stretching frequency of FeS. Optical band gap of the FeS film was determined to be 2.52 eV. Refractive index, extinction coefficient and optical conductivity of this film were determined using transmittance and reflectance spectra.