Shikonin, isolated from the root of Lithospermum erythrorhizon, showed strong cytotoxic activity against L1210(ED₅₀ = 0.06 ㎍/ml), A549(ED₅₀ = 0.78 ㎍/ml) and T/C=112% in ICR mice bearing S-180 at a dose of 5 μmole/kg/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 shikonln.