The agency says the unauthorized product, sold over the Internet as a treatment for serious diseases such as cancer, poses serious health risks if ingested.
It says MMS contains sodium chlorite, a chemical used mainly as a textile bleaching agent and disinfectant.
Health Canada says the product was sold through this website and that an alternate format of MMS, labelled as CDS, is also available for sale on the website and would pose a similar risk.
Anyone who has used the product is advised to see a doctor and report health problems to Health Canada.
The agency says it seized the product from the business, which Health Canada says has not complied after being told its product could not be sold under the Food and Drugs Act.