Previous work has shown that a number of phenolic components of NZ propolis possess antiproliferative activity against certain human gastrointestinal cancer cell lines. Here we report on a series of acylglycerols isolated from the nonpolar fraction of propolis resin, which represent further bioactive constituents unrelated to the more usual phenolic compounds generally found in propolis. NZ propolis is sourced from poplar trees, and the acylglycerols have been shown to be present in the leaves and buds of some common poplars. The compounds are a series of monoglycerides containing 3,8-dihydroxy fatty acids, many of which are further acylated with acetic acid residues. The dihydroxy fatty acids are C<sub>18</sub> to C<sub>24</sub>, with the most abundant being C<sub>20</sub> and C<sub>22</sub>. These acylglycerols were found to have strong antiproliferative activity against three human gastrointestinal cell lines, particularly gastric cancer cell line NCI-N87, where one example shows an IC<sub>50</sub> of less than 50 μM.