The authors note that fishing line is the simplest among the many types of fishing implements. The tensile strength of fishing line made of polymeric materials and the mechanical behaviors of fishing line which differ from metallic and which are complicated due to factors such as time-temperature dependency have been reported. Fishing line is hardly ever used as is, but always has a knot. In this study, therefore, the authors discuss how the knot in fishing line and the metallic swivel affect the tensile strength of the line.