To provide a polyamide monofilament ≥0.5mm in filament diameter D having high knot strength especially even in the region of the filament diameter of as thick as 0.5-1.5mm, and to provide a method for producing the same.

The polyamide monofilament 0.5-1.5 mm in filament diameter D is such one that the crystal layer orientation in the fiber section changes from the fiber surface toward the center of the section. Specifically, the orientation parameter(R) calculated from the Raman band intensity ratio determined by laser/Raman spectrometry changes from the fiber surface toward the center, the orientation parameter(R) on the fiber surface being ≤1.3 and that at a point 10μm in depth under the surface ≤1.6. In this monofilament, said filament diameter D and knot strength T(N) meet the relationship(I):T≥750D-400, and the variation CV value of said knot strength T is ≤10%.