ИСТИНА

The preliminary results of ground-based UBV photometric and CCD observations of cataclysmic variable GK Per during the outburst in autumn of 2004 are presented (the average duration of outburst is about 70 days). The system consist from a white dwarf as a primary component and evolved K2 sub-giant as a secondary and has the longest known orbital period for a classical nova,- 47.9 hours. The light curve of GK Per is determined by UBV observations and color behavior of this star is also considered. CCD observations carried out in R and B bands during the night distinctly show the existence of variability. Possible explanations of this variability are discussed.