Topological indices are the molecular descriptors that describe the structures of
chemical compounds. They are used in isomer discrimination, structure-property
relationship, and structure-activity relations. The topological indices are used to predict
certain physico-chemical properties such as boiling point, enthalpy of vaporization,
and stability. In this paper, the inverse sum indeg index is studied. This index (ISI(G)) is
defined as  dudv
du+dv
. The inverse sum indeg index of some graph operations is
computed. These operations are join, sequential join, cartesian product, lexicographic
product, and corona operation.