Silicon tetrafluoride, SiF4, is a precursor of amorphous Si-F-H semiconductors, and Si-O-F thin solid films. It is used also for preparation of films and bulk samples of silicon isotopes 28Si, 29Si, 30Si. In this study we apply both spectroscopic and gas-chromatography methods for determination of some molecular impurities in SiF4.FTIR spectroscopy. The experimental setup included a vacuum FTIR spectrometer Bruker-120HR equipped with a 20 cm cell. The spectra in the range 4500-550 cm-1 have been recorded with a resolution of 10-2 cm-1. The following impurities were detected in SiF4 gas: HF (4150-3900 cm-1), H2O (3900-3600 cm-1 and 1650-1550 cm-1), SiF3OH (3800-3700 cm-1), CH4 and C2H6 (3000-2900 cm-1), CO2 (2380-2320 cm-1), SiH3F, SiF3H, and SiF2H2 (2200-2150 cm-1), Si2F6O (870-810 cm-1). The detection limit of these impurities is within the range 0,9 ppm (CO2) 10 ppm (Si2F6O).FTMW spectroscopy. The home-made phase-switching microwave spectrometer on coherence spontaneous radiation effect was applied, operating in the spectral region 115 - 183 GHz with a resolution of 10-6 cm-1. The analytic cell was a quartz tube with a length of 1 m. The absorption lines of impurities CHF3, CH2F2, and CH3F were detected. The detection limit of these Freon impurities is 10-1-10-2 ppm.Gas-chromatography. A home-made high-vacuum gas handling system as well as extra purification of commercial high-pure carrier gas was used. To avoid SiF4 in the flame-ionization detector chamber, it was eliminated by reaction with NaF. This method allowed to detect hydrocarbons C1-C4 (methane, ethane, ethylene, propane, propylene, iso-butane, butane) in SiF4 with detection limit (2-6)10-2 ppm.