W. A. Mozart¡¥s compositions for clarinet played a significant role in the music history. Many scholars took their attention to Concerto in A major for Clarinet and Orchestra. However, the importance of Clarinet Quintet for Clarinet and String Quartet is unneglectable. According to the literature, the development of clarinet in the musical history is no earlier than the seventeenth century. Clarinet had a variety of sizes and tonalities in the beginning of development. Mozart composed lots of brilliant compositions for the combination with the clarinet in A. A. Stadler, a clarinetist, had excellent skill in playing clarinet. He cooperated with T. Lotz, an instrumental maker, extended the compass of basset clarinet lower to C. Inspired by Stadler and the invented instrument, Mozart wrote Clarinet Quintet, K. V. 581 and Clarinet Concerto, K. V. 622 for the basset clarinet. Mozart¡¦s Clarinet Quintet, K. V. 581 is undeniably important to the history of chamber music. Clarinet Quintet, K. V. 581 is composed in four movements. Harmony, form, texture, idiom and expression in every movement were discussed in Chapter3. The setting of clarinet and string quartet was also an innovation for the chamber music in his time. This setting of Clarinet Quintet became one of the standard settings which several composers tried to compose music for. Among the works, J. Brahms¡¦ Clarinet Quintet, op. 115 and M. Reger¡¦s Clarinet Quintet, op. 146 have gained the same respect as Mozart¡¦s Clarinet Quintet, K. V. 581. These works have several similarities. For example, they were all created in one or two years before the composers¡¦ death, and the inspiration for creating the music all came from the cooperation with the outstanding performers ¡Ketc. To sum up, Mozart¡¦s Clarinet Quintet, K. V. 581 is important and influential to the history of chamber music.