Tissue ligation devices and methods are provides to mechanically strangulate abnormal or undesirable tissue. Tissue ligation devices include a catheter having an outer diameter smaller than the inner diameter of a standard endoscope channel such that the catheter can be inserted into the endoscope. Tissue ligation devices also include a ligation system with an expandable hood disposed located at the distal end of the catheter. A suture extends through a lumen of the catheter and has a distal loop portion exposed outside of the expandable hood.