New camptothecin derivatives, useful as antitumor agents or intermediates therefor, of the general formula (I) ##STR1## wherein X is a lower alkyl group, and R is a hydrogen atom or the grouping -COY where Y is a linear or branched unsubstituted C.sub.1 -C.sub.18 alkyl group; a lower alkyl group substituted by a halogen atom or a lower alkylthio, amino, acylamino, hydroxyl, lower alkoxy, aryloxy or lower alkoxycarbonyl group; a C.sub.3 -C.sub.19 alkenyl, C.sub.3 -C.sub.19 alkynyl or C.sub.3 -C.sub.8 cycloalkyl group; a C.sub.3 -C.sub.8 cycloalkyl group substituted by an acylamino-lower alkyl group; an N-acylpyrrolidyl group; a phenyl group; a phenyl group substituted by a halogen atom or a trifluoromethyl, nitro, amino, lower alkoxycarbonyl, lower alkyl, phenyl or lower alkoxy; a cinnamyl group; a benzyl group; a naphthyl group; a pyridyl group; a furyl group; or a thienyl group, as well as acid addition salts and quaternary ammonium salts thereof,and a process for preparing the new camptothecin derivatives by subjecting 7-ethylcamptothecin to the treatment with an N-di-X-ethylenediamine followed by acylation.