This invention is about a water soluble antimicrobial polyacrylate silver salt. The molecular chain of the polyacrylate silver salt comprises sodium carboxylic group (—COONa) and silver carboxylic group (—COOAg). It is synthesized by dissolving an polyacrylate polymer comprising sodium carboxylic group (—COONa) in water and then exchanging the sodium carboxylic group of the polyacrylate polymer to silver carboxylic group (—COOAg) using silver salt in aqueous solution. Ultrafiltration membrane is used to remove the sodium salt generated from the metal ion exchanging procedure. An aqueous solution of water soluble antimicrobial polyacrylate silver salt with very few impurity is obtained. The water soluble antimicrobial polyacrylate silver salt is then obtain-ned from the aqueous solution. The molar ratio of —COOAg to —COONa of thus obtained water soluble antimicrobial polyacrylate silver salt can be as high as 66/34.