The ultimate goal of the Heidelberg Catechism(1563) is to secure religious reformation in Pfalz by clarifying the foundation of reformation and teaching people the direction of reformation. This study aims to manifest that the ecclesiology of the Heidelberg Catechism tries to present a clear vision of the true Church in the perspective of the reformed tradition while a hot controversy concerning the Lord Supper continued in Pfalz. For this purpose, the historical and the theological backgrounds of the Heidelberg Catechism are examined in the first place, and then the structure and the contents of the ecclesiological questions and answers in the Catechism is analysed. This investigation shows that prudent and cautious presentations about the Church in the prefatorial questions and answers in the Catechism result from the Heidelberg reformers’ endeavor to minimize the theological controversy between the Gnesio-Lutheran and the Reformed circles concerning the Lord Supper. In the following questions and answers, however, the Heidelberg Catechism deals with the three external marks of the true church such as doctrine, sacraments, and discipline. This shows that this Catechism does not fail to pursue its ultimate goal to establish and secure religious reformation in Pfalz. Therefore, it is right to evaluate that the Heidelberg Catechism was the result of the magistrates and theologians in Pfalz who proclaim and foster their vision of reformation. For the Heidelberg reformers’ who made the Catechism, it is the true Church that stands on the true doctrine of salvation, administers the right sacraments according to the Word, and carries out sincere discipline in the church.