Developments in distributed generation (DG) technologies, information and communication technologies, environmental concerns, liberalization in electricity markets and restructuring encourage operation of DGs in smart grid. High penetration of DG resources is increasing worldwide. In this paper we present an analyze of the effect of CO2 emission cost on distribution network scheduling with photovoltaic (PV) and wind turbine as power sources. The proposed model in this paper considers retail price of distribution network and price of generated electricity by PV and wind turbine. Numerical simulations are carried out used a 33-bus test distribution network. Test results show that the current policy to determine CO2 emission tax, considering the price of generated electricity by DGs, is not always supportive of operation of DGs at their maximum output.