It is an object of the present invention to provide a method for producing a conjugate of thyroxine and albumin with higher purity. The present invention provides a method for producing a conjugate of thyroxine and albumin which comprises: step (a) of converting a carboxyl group in thyroxine having a carboxyl group to be linked to albumin into an active ester and allowing the thyroxine to react with albumin, so as to prepare a conjugate of thyroxine and albumin and step (b) of purifying the conjugate with the use of an acidic mixed aqueous solvent in which the thyroxine having a carboxyl group to be linked to albumin is dissolved but albumin is not precipitated.
