New camptothecin derivatives possessing either or both of high anti-tumor activity and slight toxicity, represented by the general formula: ##STR1## wherein X is H, CH.sub.2 OH, COOH, an alkyl group, an aralkyl group or the grouping CH.sub.2 OR.sup.1 or COOR.sup.2 wherein R.sup.1 is an alkyl group or an acyl group and R.sup.2 is a lower alkyl group, Y is H, OH or the grouping OR.sup.3 wherein R.sup.3 is a lower alkyl group or an acyl group, and Z is H or an acyl group, with the proviso that when X is CH.sub.2 OH, an alkyl group or an aralkyl group, both Y and Z are H, that when X is the grouping CH.sub.2 OR.sup.1 or COOR.sup.2, Y is H, that when Y is OH, both X and Z are H, and that when Y is the grouping OR.sup.3, X is H, and water-soluble alkali metal salts thereof. These camptothecin derivatives are prepared by treating camptothecin with sulfuric acid and a persulfate or with sulfuric acid and a peroxide, if necessary, with an organic compound corresponding to the organic moiety of the substituent to be introduced directly into camptothecin, in an aqueous medium in the presence or absence of a transition metal ion, and optionally treating the resultant products, if necessary, after oxidation of the introduced substituent, with an alkylating agent or an acylating agent.