The Act of Uniformity 1548, also known as the Act of Uniformity 1549, the Uniformity Act 1548, or the Act of Equality (2 & 3 Edw. 6. c. 1), was an act of the Parliament of England, passed on 21 January 1549 during the reign of Edward VI. Formally titled An Act for Uniformity of Service and Administration of the Sacraments throughout the Realm, it mandated the use of the newly created Book of Common Prayer across England, Wales, Calais, and all other Crown territories. It was the first act of its kind, establishing a single, uniform form of Christian worship at a time when competing branches of the faith were causing widespread social unrest, including the Prayer Book Rebellion in Cornwall and the South West of England.

The Book of Common Prayer, largely the work of Archbishop of Canterbury Thomas Cranmer, was not merely a translation of existing Latin liturgical texts but a substantially new creation, reflecting a range of reforming doctrinal influences while retaining certain Catholic elements such as altars, vestments, and prayers for the dead. The act required all clergy to conduct services in accordance with the new prayer book, with penalties escalating from the loss of one year's income and six months' imprisonment for a first offence, to deprivation of all positions for a second offence, to life imprisonment for a third.

The act proved deeply controversial. When debated in the House of Lords in January 1549, eight of the eighteen bishops present voted against it, and hostility to the new prayer book prompted rioting in several parts of the country. It was superseded by the Act of Uniformity 1552, which introduced a more overtly Protestant prayer book, before being repealed under Mary I and revived in modified form under Elizabeth I by the Act of Uniformity 1558. The major principles established in 1549 were continued and developed by the Act of Uniformity 1662, passed following the restoration of the monarchy under Charles II, most of which was itself repealed during the removal of religious discrimination in the nineteenth century.

The Book of Common Prayer was far from just an English-language translation of the Latin liturgical books; it was largely a new creation, mainly the work of Archbishop Thomas Cranmer, which in its text and its ceremonial directions reflected various reforming doctrinal influences (notably the breviary of Cardinal Quiñonez and the Consultation of Hermann von Wied). Compromises were evident as well; for instance, altars were retained, along with vestments, private confessions, and prayers for the dead. The first act (2 & 3 Edw. 6. c. 1) was called An Act for Uniformity of Service and Administration of the Sacraments throughout the Realm. It deemed as follows:

This section covers the following three points. England claimed many territories as its own with the phrase "or other of the king’s dominions". And that there was plenty of time for England's territories to become accustomed to these new laws giving them approximately one year to use the Book of Common Prayer to unify the country behind a single common practice of Faith.

Then follow penalties against those of the clergy that should substitute any other form of service, or shall not use the Book of Common Prayer, or who shall preach or speak against it:

This provided loss of all income, which was forfeited to the Crown. Imprisonment "without bail or mainprize" meant one could not pay one's way out of prison, nor be given freedom until acquittal or the completion of the sentence.

A second offence was dealt with more harshly: