Recently, the restructuring of electricity market and the development of technology have been enhancing the application of distributed generators and renewable energy resources. Hence, the planning of distribution systems for competitive electricity markets has encountered impacts which need to be investigated. The paper proposes a new model for distribution systems planning in a competitive electricity market that can determine equipment sizes and timeframe of distribution systems, technology selection and installation period of distributed generators. The model uses the objective function that minimizes the total cost of network upgrading, new distributed generators installation, distribution systems operating, and electric energy purchasing from markets. The proposed model is tested using an 48 bus 22kV radial feeder. The calculation is programmed in GAMS environment.