Abstract: Four new octadecanoid derivatives ( 1-4 ) including a pair of enantiomers ( 1/2 ), along with 12 known analogues ( 5-16 ), were isolated from the seeds of Ipomoea nil. Their structures were determined by detailed spectroscopic analyses and comparison with reported data of structurally related compounds, with the absolute configurations of 1 and 2 being assigned by an in situ dimolybdenum ECD method. Our bioassays revealed that these isolates did not show ABTS radical scavenging activity while 10 and 13 displayed better α-glucosidase inhibitory activity than the positive control acarbose (IC₅₀ 167.7 ±1.55 μmol·L^-1), with IC₅₀ of 92.73 ±3.12 and 11.39 ±2.18 μmol·L^-1, respectively.