Data mining is the process of extracting knowledge hidden from large volumes of raw data. One of the technique in data mining is association rule, while a priori is one of association rule techniques. In this paper, we try to implement a priori algorithm to get association rules among Northwind data, a sample database comes with SQL Server 2000 packages, as secundey data. The result of this research is an application that can generate association rule among the products in Northwind. The application is designed to generate association rule until n-antecedent with one consquent. However, because of count of data in Nortwind is not great enough, in testing only get association rule with one antecedent and one consquent. In this article, we explains how to implement a priori algorithm. The implementation explained in step by step detail to picture out the development process of application program that use a priori.