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 (IC 50 167.7 ± 1.55 μmol-L −1), with IC 50 of 92.73 ± 3.12 and 11.39 ± 2.18 μmol-L −1, respectively.