The efficient synthesis of novel 3-aminohexahydrocoumarin derivatives with high diastereoselectivity, wide applicability, short reaction time, high yields as well as operational simplicity was achieved via microwave-assisted reactions of dimedone or cyclohexane-1,3-dione with 4-arylidene-2-phenyloxazol-5(4H)-ones. Moreover, these novel compounds were subject to the test of in vitro cytotoxicity to carcinoma SW1116 and SGC7901 cells. Seven compounds showed stronger cytotoxicity to carcinoma SW1116 cells than doxorubicin hydrochloride at the concentration of 10 ug/mL. Nearly all the tested compounds exhibited strong or moderate cytotoxicity to SGC7901 cells with IC 50 values from 5.127 to 0.158 ug/mL.