Unit Commitment (UC) is used to schedule generators such that the total system production cost over the scheduled time horizon is minimized under the spinning reserve and generator operational constraints. UC problem is a nonlinear, mixed integer combinatorial optimization problem. The global optimal solution can be obtained by complete enumeration, which is not applicable to large power systems due to its excessive computational time requirements. This paper solves a Unit Commitment (UC) problem of the interconnected power system. The UC provides an approach to decrease the cost and improve reliability of the network. The UC is a dynamic process, and the generation plan is always changing according to different load and network topology. The problem is solved by Dynamic Programming approach which solves the dynamic problem in 12 stages. In this work, a large scale Unit Commitment (UC) problem has been solved using Dynamic programming without time constraints and the results show the comparison of production cost.