Constant growth of distributed generation (DG) in power systems has not only positive changes. Incorrect placement of DG can worsen steady-state parameters of a power grid, for example, power losses. The specific mathematical model and approach of optimal DG placement and capacity have been developed. To solve the problem of DG optimal placement and capacity the system of constraints and optimization criteria has been proposed. Objective function on basis of the proposed system allows evaluating the optimality of solution. The developed approach using Monte-Carlo method has been tested on IEEE 14-bus test system. The results of simulation tests show viability of the developed approach.