A method for preparing trishydroxymethyl phosphine from tetrakishydroxymethyl phosphonium salt, the method including at least the steps of continuously feeding a first reaction chamber with, from one hand, at least one tetrakishydroxymethyl phosphonium salt and, from another hand, at least one base, under conditions suitable for a reaction of the tetrakishydroxymethyl phosphonium salt(s) with the base(s), to form a mixture of trishydroxymethyl phosphine and formaldehyde; and continuously removing the formaldehyde.