Isadora Duncan indicates in The Art of the Dance the importance of her childhood experiences in the establishment of her own new dance style. However, her early dance career, before leaving the United States in 1899, is somewhat mysterious. Therefore, this paper examines what kind of dance she studied in her childhood and the process of how she created her own dance style. It discusses her early performances in the United States, especially in New York, by utilizing the unpublished memoir of her brother, Raymond Duncan, as well as newspapers of the time.