The duo module plays an important role in the module theory. Many researchers generalized this concept such as Ozcan AC, Hadi IMA and Ahmed MA. It is known that in a duo module, every submodule is fully invariant. This paper used the class of St-closed submodules to work out a module with the feature that all St-closed submodules are fully invariant. Such a module is called an Stc-duo module. This class of modules contains the duo module properly as well as the CL-duo module which was introduced by Ahmed MA. The behaviour of this new kind of module was considered and studied in detail,for instance, the hereditary property of the St-duo module was investigated, as the result; under certain conditions, every St-closed submodule of an St-duo module is also St-duo. Another characterization of the Stc-duo module was given. Additionally, the relationships of St-duo among some types of modules were investigated and discussed, for example; In the class of semi-extending modules, every weak duo module is anStc-duo module.Also, the authors gave a case in which St-duo, duo, CL-duo and weak duo are equivalent. Furthermore, the St-duo module was used to make the concepts semi-extending and FI-extending equivalent
