Provided are a water-soluble triarylphosphine for a palladium catalyst, which has high selectivity in a telomerization reaction and is easily recovered with efficiency, an ammonium salt thereof, and a method for efficiently producing the same. Specifically, provided are bis(6-methyl-3-sulphophenyl)(2-methylphenyl)phosphine; a bis(6-methyl-3-sulphonatophenyl)(2-methylphenyl)phosphine diammonium salt obtained by reacting the phosphine with a tertiary amine having a total of 3 to 27 carbon atoms in groups bonded to one nitrogen atom; and a method for producing the same.