This musical analysis is mainly to explore the musical form of the piece, Piano Sonata in Bb major, K. 333, first movement by Wolfgang Amadeus Mozart. The purpose of this analysis is to reveal the design and harmonic organization of this piece. Besides that, the techniques that contribute to the continuous unbroken flow of musical ideas in the piece are examined. Finally, the interplay between tension and relaxation happened in the piece is discussed too. Score analysis and observation technique are applied in this study. The phrase structural organization is fundamental in this analysis....