Mucoid plaque (or mucoid cap or rope) is a pseudoscientific term used by some alternative medicine advocates to describe what is claimed to be a combination of harmful mucus-like material and food residue that they say coats the gastrointestinal tract of most people. The term was coined by Richard Anderson, a naturopath and entrepreneur, who sells a range of products that claim to "cleanse" the body of such purported plaques.

Many such "colon cleansing" products are promoted to the public on websites that have been described as making misleading medical claims. The presence of laxatives, bentonite clay, and fibrous thickening agents in some of these "cleansing agents" has led to suggestions that the products themselves produce the excreted matter regarded as the plaque. The concept of a 'mucoid plaque' has been dismissed by medical experts as having no anatomical or physiological basis.