Description: The paper proposed a mathematical model to optimize the stock of spare parts and materials. It aims to determine the volume and number of deliveries, which maintain the required stock so that the total cost P(Q) for the planned period be minimal. A study of the proposed model is made, using data on consumption of spare parts for electrical equipment for tractors. The model is applicable to agricultural and commercial organizations and makes it possible to manage stocks in them. The overall demand from stocks and the costs of transport and processing of a service influence most on the total cost for maintaining of stocks and the optimized parameters