Studies were made the possibilities of increasing the wave-dispersive X-rayfluorescence spectrometer analytical characteristics due to using the superfine beryllium foils5-8 μm thick in the X-ray detector. Investigations by the example of spectrometerSPECTROSCAN MAX-GVM showed that the decrease of foil thickness can significantlyincrease the spectrometer analytical characteristics in the determination of light elements(sodium and magnesium). It has been established what count rate increases 8.5 times for sodium and 4.6 times for magnesium due to using the X-ray windows with thickness of 5 and8 μm. Reducing of X-ray window thickness can be achieved by using beryllium foils obtained by severe cold plastic deformation. Such foils have increased plasticity, which allowsreducing the X-ray window thickness without spectrometer reliability decreasing.