The one- and two-neutron removal reactions from (17)C and (18)C as well as the reaction cross section of (18)C have been studied using a carbon target at 80A MeV. The longitudinal momentum distributions of (15,16)C fragments from (17)C and (16,17)C fragments from (18)C were measured by a direct time-of-flight method. The width of (15)C fragments from (17)C is fairly smaller than that from other C isotopes. The experimental data are discussed within the framework of the Glauber model.