New Camptothecin derivatives possessing high anti-tumor activity with slight toxicity, represented by the general formula: ##STR1## wherein R.sup.1 stands for a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxy group or an acyloxy group, R.sup.2 for a hydrogen atom, an alkyl group, an aralkyl group, a hydroxymethyl group, a carboxymethyl group or an acyloxymethyl group, and R.sup.3 for the grouping --XR' (where R' is a hydrogen atom, an alkyl group or an acyl group and X is an oxygen atom or a sulfur atom), a nitro group, an amino group, an alkylamino group, an acylamino group or a halogen atom, with the proviso that when both of R.sup.1 and R.sup.2 are hydrogen atoms, R.sup.3 should not be hydroxyl group, methoxy group or acetoxy group. These new camptothecin derivatives are prepared by treating a 5-R.sup.1 -7-R.sup.2 camptothecin derivative with a peroxidant and then reacting the resultant 5-R.sup.1 -7-R.sup.2 -camptothecin-1-oxide with an active hydrogen compound under irradiation of UV-rays or by catalytically hydrogenating the ring B of camptothecin in a solvent, treating the resultant tetrahydro product with an acylating agent, introducing nitro group into 10-position of the acylated product by the reaction with nitric acid, splitting off the acyl group in the 10-nitro product by hydrolysis and treating the hydrolyzed tetrahydro product with an oxidizing agent for dehydrogenation, and if desired, reducing the nitro group in the resultant product to amino group and modifying the amino group by N-alkylation, N-acylation or by diazotization followed by hydrolysis or Sandmeyer reaction, before or after the oxidation of the 10-nitro-tetrahydro product.