A new series of monomer and dimer derivatives of dihydroartemisinin (DHA) containing substituted chalcones as a linker were synthesized and investigated for their cytotoxicity in human cancer cell lines HL-60 (leukemia), Mia PaCa-2 (pancreatic cancer), PC-3 (prostate cancer), LS180 (colon cancer) and HEPG2 (hepatocellular carcinoma). Some of these derivatives have greater antiproliferative and cytotoxic effects in tested cell lines than parent compound DHA. The structures of the all compounds were confirmed by IR, ¹H NMR and mass spectral data. Among the new derivatives, compounds 8, 14, 15, 20 and 24 were found to be more active than parent DHA against tested human cancer cell lines. DHA derivatives were found to be most active in human leukemia cell lines with compounds 8, 14, 15, 20 and 24 showed IC₅₀ values less than 1 μM for 48 h whereas DHA has IC₅₀ value of 2 μM at same time period. The most potent compounds 8 with IC₅₀ = 0.3 μM (at par with doxorubicin (IC₅₀ = 0.3 μM)) and 15 with IC₅₀ = 0.4 μM, of the series, six and three times active than DHA (with IC₅₀ = 2 μM) respectively were selected for further mechanistic work in human leukemia HL-60 cells.