The 11C-radioisotope is used to label either methanol or methyl iodide for distinction of individual methyl group in their co-reaction on Fe-H-Beta-300 zeolite. The adsorption and desorption of 11-labeled compounds and its derivates on catalyst were followed-up by radiodetectors. The gas chromatograph FID detector on-line with a flow radioactivity detector was used to determine the origin of methyl groups in the co-reaction. The results present dimethyl ether and some hydrocarbons as co-products over light acid sites of Fe-H-Beta-300. Moreover, the radio-GC analysis confirms that, using 11C-methanol co-reaction with methyl iodide, a newly formed radioactive compound, i.e. 11-methyl iodide was radiodetected from 11C-methyl fragment of methanol. This methyl exchange, as a co-reaction of 11-methanol with methyl iodide, can be detected by only radiolabeling, hereby the origin of the newly synthesized methyl iodide is manifested.