Abstract: A mixing and kneading device comprises a mixing and kneading shaft mounted in a housing and driven to a rotating as well as to a reciprocating movement. For sealing the housing, there is provided a sealing assembly located between the housing and the mixing and kneading shaft. The sealing assembly includes a supporting assembly arranged between the housing and the mixing and kneading shaft and provided with first and second sealing means. The supporting assembly is locked against rotation, but coupled to the mixing and kneading shaft to perform therewith its reciprocating movement. The first sealing means serves for rotatively seal the mixing and kneading shaft and is located between the mixing and kneading shaft and the supporting assembly. The second sealing means provides for a translative sealing of the mixing and kneading shaft and is located between the supporting assembly and the housing.