In the 17th and 18th centuries, to satisfy the demand for weaponry, military supplies, and luxury items, the Lê-Trịnh government opened its ports to Western merchant ships trading in the Tonkin market. Consequently, Christianity found an opportunity to reach Đại Việt along with Western missionaries who traveled on board these trading vessels. Initially, the missionaries and the Christian religion were welcomed. Therefore, the missionaries achieved quite promising evangelist results. However, around 1650s onwards, due to political and national security reasons, the Lê-Trịnh court imposed a ban on Christianity and showed inconsistency towards Western missionaries. At the same time, the civil war with Cochinchina ended in 1672, lessening the urgency of the Lê-Trịnh court’s needs for weaponry and military supplies compared to earlier periods. Christianity was thus regarded as a heretical religion by the authorities and was strictly banned. This article aims to clarify the status of Christianity in Tonkin and the state’s reactions, thereby revealing the pragmatism and opportunism of the Lê-Trịnh period during the 17th and 18th centuries.In the 17th and 18th centuries, to satisfy the demand for weaponry, military supplies, and luxury items, the Lê-Trịnh government opened its ports to Western merchant ships trading in the Tonkin market. Consequently, Christianity found an opportunity to reach Đại Việt along with Western missionaries who traveled on board these trading vessels. Initially, the missionaries and the Christian religion were welcomed. Therefore, the missionaries achieved quite promising evangelist results. However, around 1650s onwards, due to political and national security reasons, the Lê-Trịnh court imposed a ban on Christianity and showed inconsistency towards Western missionaries. At the same time, the civil war with Cochinchina ended in 1672, lessening the urgency of the Lê-Trịnh court’s needs for weaponry and military supplies compared to earlier periods. Christianity was thus regarded as a heretical religion by the authorities and was strictly banned. This article aims to clarify the status of Christianity in Tonkin and the state’s reactions, thereby revealing the pragmatism and opportunism of the Lê-Trịnh period during the 17th and 18th centuries.