The existence of many molecules in the form of clathrate hydrates (CHs) in ultrahigh vacuum (UHV) and cryogenic conditions has not been explored adequately. In the present study, a detailed investigation by reflection absorption infrared spectroscopy confirmed that the three phases of ethane, i.e., amorphous, crystalline, and CH, coexist in a vapor-deposited ethane-water mixture at 60 K in UHV. Experiments were conducted with vapor-deposited ice films at 10 K, which were annealed to 60 K for tens of hours, and the IR spectral evolution was monitored systematically. Upon maintaining the system at 60 K, three phases of ethane were seen to coexist, but a gradual increase in the hydrate phase was noticed. The evolution of ethane CH from the amorphous ethane-water ice mixture was observed for the very first time in UHV under cryogenic conditions. The formation of the CH was further confirmed by temperature-programmed desorption (TPD) mass spectrometry. Quantum chemical calculation suggested the formation of 51262cage of structure I CH in the ice matrix. The formation of ethane CH in a thin ice film at such a low temperature under UHV suggests its existence in the cometary environment. © 2022 American Chemical Society. All rights reserved.