In preparing an iodoalkynyl carbamate by iodinating an alkynyl carbamate with iodine monochloride in water or a solvent mixture composed of water and an organic solvent in the presence of a base, the iodoalkynyl carbamate can be obtained in a yield of as high as 96 to 98% by using the alkynyl carbamate in a concentration of 5 to 20% by weight, dissolving the iodine monochloride in an aqueous solution of hydrochloric acid or an aqueous solution of an alkali metal chloride (the amount of iodine monochloride used being within the range of 1.0 to 1.2 moles per mole of the alkynyl carbamate and the amount of base used being within the range of 0.95 to 2.00 gram equivalents per mole of iodine monochloride), and carrying out the reaction at a temperature of 10.degree. to 40.degree. C. for a period of 1 to 4 hours.According to this process, highly pure iodoalkynyl carbamates which are useful as industrial germicides can be prepared with good selectivity and in high yield.