Based on the structure of 23-hydroxybetulinic acid (1), a series of 28-amide derivatives were synthesized. Biological evaluation in vitro for their antitumor activities against five cell lines (A549, BEL-7402, SF-763, B16 and HL-60) has indicated that compound 6g possesses the most effective antitumor activity with an IC50 value of 10.47 μM when treated with HL-60 cells. In vivo testing has also shown a comparable activity of 6g to cyclophosphamide against H22 liver tumor in mice and 5-fluorouracil against B16 melanoma, respectively.