The Council of 325 is regarded as the first ecumenical church assembly in history. The creed formulated there is still accepted today as binding across the boundaries of Christian denominations.
The congress, which will be attended by scientists from four continents and several Christian churches, will initially take place at the Pontifical Gregorian University. It will continue on 17 October at the University of Münster.
Speakers on the first day included Münster's Professor of Ancient Church History, Alfons Fürst.
He examined the various theological approaches that preceded the Creed of Nicaea in late antiquity.
As a result, he criticised that the formula of faith found in Nicea about the equality of God and Jesus Christ was unbalanced. It had led to Christianity assuming for a long time that there was too wide a gap between God and his creation.
A meeting between the participants and Pope Francis planned for Saturday at the end of the congress was cancelled due to the current illness of the head of the Church.
To mark the 1,700th anniversary of the Council, an anniversary celebration is planned for May at the historic site, which is now located in Turkey.
The head of honour of the Orthodox churches, Patriarch Bartholomew, and Pope Francis, among others, were due to attend.
Last week, there was a preparatory meeting with Vatican staff at the official residence of the honorary head of world Orthodoxy in Istanbul.