The invention relates to a method for producing a binder composition, wherein the method comprises: a) preparing a prepolymer of resorcinol and glyoxal by allowing resorcinol to react with glyoxal in an aqueous composition; and b) mixing the prepared prepolymer and alkalated lignin, wherein the alkalated lignin has an alkalinity of 1-10 weight-%, at a temperature of 15-30°C to allow the prepared prepolymer to react with the alkalated lignin until a binder composition with a predetermined viscosity value is formed, wherein the molar percentage of the amount of alkalated lignin to be mixed with the prepared prepolymer to the total amount of alkalated lignin to be mixed with the prepared prepolymer and of resorcinol used for the preparation of the prepolymer is at least 60 %.