Abstract: A stop knot tying device which aids with tying a stop knot directly on a fishing line for use with a slip bobber. The stop knot tying device generally includes a main body having a retainer portion and an elongated portion extending therefrom. The retainer portion includes a ring member and funnel member which act to retain a coil of string. A distal, free end of the coil of string exits the retainer portion through an aperture on its ring member. The elongated portion includes a slot running along its length and at least one notch. By positioning a fishing line within the slot through one of the notches and winding a cut-away portion of string around the line, one can utilize the present invention to efficiently and safely tie a stop knot on a fishing line.