Nylon 6 a metal replacement material that has high heat resistance properties. With these properties, such as Nylon 6 is widely used in the fields of transport, health, and is used for materials research. Although Nylon 6 has good manufacturing properties, to create complex parts joining technology can be utilized. The technology is often used for connecting Nylon 6 is the connection technology of adhesive (glue), but this connection still has many shortcomings, it takes another alternative connection. FSW is an innovation in the field of welding grafting. FSW is a solid connection technique (solid-state) that is generally used for joining two materials by utilizing a heat source of friction going on their rotary tool and stirring the melt to form a connection. FSW can reduce the differences in the melting point can not connect to fusion welding. Not only metal, but this method can also be used on plastic material such as the type of Nylon 6. purpose of this study was to determine the effect of variations in the ratio of the diameter of the tool and tool rotational speed of the tensile properties on the connection Nylon 6 with the welding method FSW. In this study was used Nylon 6 with dimensions of 115 mm x 100 mm and a thickness of 4 mm. The parameters used are variations in tool diameter ratio of 10/3, 15/3, 20/3 and tool rotational speed 5800 rpm, 6000 rpm, 6200 rpm, with a feedrate of 4 mm/min, and a tool made of steel ST80. Results of welding are cut using a water jet, in according to ASTM D638 standard type-4. Characterization was, then testing is carried out including testing macro image, hardness testing, and tensile testing. In general, there is still a defective weld that affects the tensile properties of connection in this study. Tensile testing results showed that the variation parameter tool diameter ratio 15/3 with 5800 rpm rotational speed tool shows the value of the highest tensile strength of the weld is equal to 10,2 MPa, but the value is still below the value of the tensile strength of the raw material 21,3 MPa, and the lowest tensile strength results are shown in the variation of tool diameter ratio of 20/3 with parameter tool rotational speed of 6000 rpm by 2,76 MPa. The test results showed that the specimens hardness which has the highest tensile strength value of the weld level reached 62,5 shore D hardness, whereas the specimen which has the lowest value of the tensile strength of the weld hardness 44,5 shore D. In terms of the macro picture is still a weld defect such as defect indication fusion incomplete or crack defects affecting the mechanical properties of most of the weld. The results show that has been done, the tool diameter ratio variations with a high rotational speed can replace heating tools and better results.