Although there is a tendency worldwide towards alternative methods in effectively managing weeds, use of herbicides to control weeds in conventional agriculture is still inevitable. With regard to externalities (through unsystematic use of herbicides) imposed upon environment, in the present paper it has been tried to study the willingness to pay of wheat farmers to plan for reducing the side effects of herbicides (in the form of different measures) and by use of a cross sectional data set related to wheat farmers in 2008 in Khorasan Razavi Province. A contingent valuation method was employed in the course of implementation of the study. To achieve the purpose, 180 farmers from different cities of the province were selected through random sampling method. Data were collected through questionnaire. Results showed that average willingness to pay of farmers to reduce externalities of herbicides is about 238733.3 Rials ha-1 which is higher than the cost of herbicides (150833.3 Rials ha-1). Also, by change in the choices of reducing externalities of herbicides on different environmental components, the level of willingness to pay of farmers increased. In addition, age, knowledge of farmer and ownership exert positive effects on willingness of farmers to pay to reduce the externalities of herbicides. Also, there is a significant positive correlation between education level along with type of ownership and average willingness to pay to reduce the environmental externalities of herbicides. Results indicate that the efforts of experts to produce herbicides with minimum negative side effects, taking into consideration the rate of willingness to pay in the system of pricing and in herbicide provision effective mechanisms for informing farmers are in the meantime strongly recommended.