The feasibility of antisolvent crystallization by means of gas-liquid slug flow in curved microchannels is examined in this study. The present flow regime and channel design are employed to avoid the stratified flow of a solution and antisolvent where sufficient mixing cannot be expected. DL-Threonine in water is crystallized with ethanol (antisolvent) as a model study on high-value amino-acid crystallization. Air is used as the carrier fluid, since ethanol is soluble in organic liquids, which were used as the carrier fluids for salting-out proteins in microchannels in the literature. It is found that a sudden increase in the channel width after the confluent point of gas and liquid streams results in the stable formation of slugs, but the length of the slugs varies to some extent. However, it seems that effective mixing is achieved in the slugs regardless of their length. The degree of supersaturation is adjusted by changing the ratio of threonine aqueous solution to ethanol flow rates such that the total flow rate remains constant. It is shown that antisolvent crystallization in curved microchannels is feasible and effective in controlling the crystal shape and size. The characteristics and potential for antisolvent microcrystallization is discussed, and it is compared with crystallization without mixing in microchannels.