The Hu chemical attacks occurred on 3 June 1963, when soldiers of the Army of the Republic of Vietnam (ARVN) poured liquid chemicals from tear gas grenades onto the heads of praying Buddhists in Hu, South Vietnam. The Buddhists were protesting against religious discrimination by the regime of the Roman Catholic President Ng nh Dim. The attacks caused 67 people to be hospitalised for blistering of the skin and respiratory ailments.

The protests were part of the Buddhist crisis, during which the Buddhist majority in South Vietnam campaigned for religious equality after nine people were killed by government forces while defying a ban that prevented them from flying the Buddhist flag on Vesak. The incident prompted the United States to privately threaten to withdraw support for Dim's government and when the Americans finally reduced aid a few months later, the army took it as a green light for a coup. An inquiry determined that the chemical used in the attack was a liquid component from old French tear gas grenades that had never functioned properly. The findings exonerated the ARVN soldiers from charges that they had used poison or mustard gas. The outcry over the attack had already forced Dim to appoint a panel of three cabinet ministers to meet with Buddhist leaders for negotiations regarding religious equality. The talks led to the signing of the Joint Communique, but the policy changes it provided were not implemented and widespread protests continued, leading to the assassination of Dim in a military coup.

The Buddhist crisis (Vietnamese: Biến cố Phật giáo) was a period of political and religious tension in South Vietnam between May and November 1963, characterized by a series of repressive acts by the South Vietnamese government and a campaign of civil resistance, led mainly by Buddhist monks.The crisis was precipitated by the shootings of nine unarmed civilians on May 8 in the central city of Huế who were protesting a ban of the Buddhist flag. The crisis ended with a coup in November 1963 by the Army of the Republic of Vietnam (ARVN), and the arrest and assassination of President Ngô Đình Diệm on November 2, 1963.