In this article, Chopin's Fantasie-Impromptu (Op. Posth. 66) has been analyzed both structually and harmonically. Fantasie-Impromptu, is one of the most performed piece among Chopin's other works and the major beauty is because it is based on a balanced form. In this piece, each section is separated into sub-sections and outlined schematically. This study will absolutely make the pianists to perform this piece more consciously and needless to say, gain the ability and be able to carry out and express what the composer's conception was.