Many reports indicate that $18{eta}$-glycyrrhetinic acid ($18{eta}$-GA) from Glycyrrhizae Radix has anti-inflammatory and immunoregulatory activities, whereas reports regarding anticancer activity of the compound are few. In present study, we investigated antitumor effect of $18{eta}$-GA on tumor caused by A549 cancer cell in mice. Data resulting from the cytotoxicity assay showed that $18{eta}$-GA caused killing of A549 cells. $LD_{50}$ values of $18{eta}$-GA were app. 180 ${mu}M$ and 80 ${mu}M$, corresponding to 48 hr- and 72 hr-treatments, displaying that the killing activity was more effective as the $18{eta}$-GA treatment was prolonged. Based on these data, antitumor effect of $18{eta}$-GA was tested in nude mice. For induction of the tumor, A549 ($3{ imes}10^6$ cells/mouse) was injected subcutaneously into the lateral abdomen of nude mice (Balb/c nu/nu). To determine the antitumor effect, nude mice with tumor were given $18{eta}$-GA (1 mg/200 ${mu}l$/mouse) intraperitoneally every three days for four times. Tumor-sizes were measured with a caliper for a period of 24 days. Results showed that the $18{eta}$-GA treatment reduced the tumor-sizes (P<0.05) as compared with negative control nude mice that received diluent (DPBS). The reduction degree was greater than reduction degree by doxorubicin (60 ${mu}g$/mouse), and the pattern of reduction was almost sustained during the entire period of the observation. In conclusion, our studies demonstrate that $18{eta}$-GA has antitumor activity to the A549 cancer cell-caused tumor.