A series of novel isoindoline-1,3-diones containing 1,2,4-triazole moiety were synthesized via a one-pot reaction. Bioassay indicated that compounds 33, 35, 37 and 39 exhibited much higher activities against Botryodiplodia theobromae than commercial fungicide triadimefon at the dosage of 150 mg/L. Most interestingly, compounds 36, 37 and 45 displayed much stronger antitumor activities against four human cell lines than positive control Fluorouracil. Particularly, compound 37 had four-fold improvement compared to Fluorouracil in inhibiting A549 and HepG2 cell proliferation with IC(50) values of 6.76 and 9.44 μM, respectively. Further flow-activated cell sorting analysis revealed that compound 37 displayed apoptosis-inducing effect on HepG2 cells in a dose-dependent manner. These encouraging results could be helpful for the development of new antitumor compounds.