Abstract: Purchasing and production are important operations for enterprises. Also they have close interaction and it is better to consider them simultaneously. For this purpose, a mathematical model for integrated scheduling optimization is developed. The scheduling includes lotsizing, purchase scheduling, and production scheduling. With this model, a solution method is proposed by combining genetic algorithm with network optimization methods. In the method, chromosome of genetic algorithm provides a framework of lotsizing and production scheduling, while the network model presents purchase scheduling. Numerical results show an excellent performance of the proposed method and it outperforms the traditional hierarchical optimization strategy.