Abstract: Howiinol(GHM-10) is a new compound isolated from Goniothalamus howii. Previous studies showed that GHM-10 significantly inhibited the growth of cancer cells both in vitro and in vivo. In the present study, the characteristics of the inhibitory effect of GHM-10 on L1210 cells was investigated. The results showed that the IC₅₀ of L1210 cells treated with GHM-10 for 1h, 24h, and 7d was 6.85, 3.32 and 1.59 μg·ml^-1, respectively. This outcome is in compliance with the hypothesis that GHM-10 is a cell cycle nonspecific cytotoxic drug. When L1210 cells were treated with 1～2 μg·ml^-1 of GHM-10 for 24 h, the growth rate and mitotic index were decreased and the morphology of cell nuclei changed, but the cell viability remained at the level of 96% or more, indicating that GHM-10 mainly inhibited cell proliferation. The cell cycle kinetics of L1210 cells were studied by using a flow cytometer. The results showed that the transition of cells from G₁ phase to S phase was blocked to certain extent by the treatment of GHM-10 4 μg·ml^-1 for 12 h. The fluidity of cell membrane was also increased when the L1210 cells were exposed to 2～3 μg·ml^-1 of GHM-10 for 24 h.