Using the high resolution spectra secured with the Nasmyth Echelle Spectrograph NES of the 6 meter telescope we analysed the hydrogen-deficient binary star KS Per .
The atmospheric parameters derived are : T _ { eff } = 9500 \pm 300 K , \log g = 2.0 \pm 0.5 , and \xi _ { t } = 9.5 \pm 0.5 km s ^ { -1 } .
The hydrogen deficiency is H/He = 3 \cdot 10 ^ { -5 } , iron abundance is reduced by 0.8 dex , nitrogen abundance is very high [ N/Fe ] = 1.4 , but carbon and oxygen abundances are low .
The star luminosity is \log L / L _ { \odot } = 3.3 .
A complex absorption and emission structure of the Na I D doublet was revealed .
We suggest that the emission component forms in the circumbinary gaseous envelope .