By two results of K?the and Cohen-Kaplansky, we know that for a commutative ring, every R -module is a direct sum of completely cyclic modules if and only if every R -module is a direct sum of cyclic modules if and only if R is an Artinian principal ideal ring. Also a result of Nakayama and Skornyakov states that a ring R an Artinian serial ring if and only if every left (right) R -module is serial. Instead of considering rings for which all modules are direct sums of completely cyclic (uniserial respectively) modules, we weaken this condition and study the rings R for which it is assumed only that the ideals of R are direct sums of completely cyclic (uniserial, respectively) modules In this thesis, we describe commutative rings whose proper ideals are direct sums of completely cyclic modules. Also we study commutative rings R whose maximal ideals are direct sums of completely cyclic modules. Finally we characterize the structure of commutative rings R for which every proper ideal of R is serial