Shikonin, isolated from the root of Lithospermum erythrohizon, showed strong cytotoxic activity against L1210(ED_(50) = 0.06 ㎍/㎖), A549(ED_(50) = 0.78 ㎍/㎖) and T/C=112% in ICR mice bearing S-180 at a dose of 5 μmole/㎏/day. Five shikonin derivatives were synthesized and their antitumor activities were evaluated. The alkylation of 1`-OH and acylation of Ar-OH in shikonin increased that their antitumor activities in vivo, while decreased cytotoxicity in vitro compared with shikonin.