A method for producing an amylose-containing rayon fiber, comprising the steps of: mixing an aqueous alkaline solution of amylose with viscose to obtain a mixed liquid, spinning the mixed liquid to obtain an amylose-containing rayon fiber, and bringing the amylose-containing rayon fiber into contact with iodine or polyiodide ions, thereby allowing an amylose in the amylose-containing rayon fiber to make a clathrate including the iodine or polyiodide ions, wherein the amylose is an enzymatically synthesized amylose having a weight average molecular weight of 3×104 or more and 2×105 or less. A method for collecting iodine from brackish water with high efficiency utilizing the amylase-containing rayon fibers.