An evolution pre-Christian believes of Slavic people is explored on the basis of becoming a rite of ancient Kupala's holidays. The author does an effort to clear up the sources and essence of celebration of European Ivan's Day on the basis of different type of hisnorica sources, and also points following by thesis about the onli Goddes of ancient Slavic religion, as with the change of world views of ancient population of Ukraine Kupalian ritual changed.