The first movement is in sonata form. The first theme starts in B♭ with a conversation between the first violin and the cello. After a while the second violin takes over the conversation from the cello. It then modulates to the dominant of F major and then F minor for the second theme at around m. 45. After a repeat of the first and second themes, the development section starts in F major. It starts by focusing on the "turn" figure of the first theme. It then shifts to D major and on to G minor and eventually returns to F major before shifting to B♭ for the recapitulation. This time around the second theme stays in B♭. The movement ends without a coda.

Date of composition 1800
First published 1801
Type String Quartet
Tonality B-flat Major
Catalogue Op. 18
Instruments Violin
Viola
Cello
Autotranslations beta Ludwig van Beethoven: Six String Quartets n°6 en si bémol majeur, Op. 18
Ludwig van Beethoven: Six String Quartets n. 6 in si bemolle maggiore, Op. 18
Ludwig van Beethoven: Six String Quartets Nr. 6 B-dur, Op. 18