Abstract
The following article deals with the influence of secularization in the nineteenth century on the First Vatican Council held between 1869 - 1870, events on the Council, and especially on the wording of two important documents approved by the Council - the Constitution of the Faith Dei Filius and Constitution on the Church Pastor Aeternus.In conclusion, the article summarizes the impact secularization had in the nineteenth century not only on the ideas of the First Vatican Council, but on thinking within the whole Catholic Church, and what were its consequences in the years that followed.