A camptothecin derivative comprising a compound of the formula [I]: wherein R1, R2, R3, R4 and R5 are (A) adjacent two groups combine to form alkylene, or both are H, and one of the remaining three groups is —Xn-Alkm-R6, and the other two are H, alkyl or halogen, or (B) adjacent two groups combine to form alkylene, and one of the carbon atoms of said alkylene group is substituted by —Xn-Alkm-R6, and the remaining three groups are H, alkyl or a halogen, and one or two —CH2— of the alkylene in (A) or (B) may optionally be replaced by —O—, —S— or —NH—, X is —O— or —NH—, Alk is alkylene, or —OH, m and n are both 0 or 1, or m is 1 and n is 0, which camptothecin compound is 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 and are useful as a medicament.