Abstract: A camptothecin derivative comprising a compound of the formula ?I!: ##STR1## wherein R.sup.1 is a substituted or unsubstituted lower alkyl group, X.sup.1 is a group of the formula: --NHR.sup.2 (R.sup.2 is a hydrogen atom or a lower alkyl group) or a group of --OH, and Alk is a straight chain or branched chain alkylene group having optionally an oxygen atom in the chain thereof, bound to a polysaccharide having carboxyl groups via an amino acid or a peptide, or a pharmaceutically acceptable salt thereof. Said camptothecin derivatives show enhanced antitumor activities but few side effects unlike conventional anticancer agents, and hence, these compounds are extremely useful as a medicament.