Chitosan is a widely available, nontoxic, biodegradable biopolymer that binds negatively charged molecules. Its use as a dietary supplement for weight loss derives from its purported ability to bind negatively charged lipids and bile acids and prevent their gastrointestinal absorption. Here, we report the case of a dialysis patient who did not tolerate prescription phosphorus binders and who has been able to control her serum phosphorus levels for a year by taking 3.5 g of chitosan a day with meals. A quantitative analysis shows that chitosan may bind between 16 and 41 mg of phosphorus per gram, comparable to prescription binders. Chitosan may provide an over‐the‐counter alternative as non‐calcium phosphorus binder for patients not tolerating prescription phosphorus binders because of side effects, cost, or efforts to limit their medication burden.