The services will take place at 11:00 GMT on 7 January.
The Church in Wales announced the move ahead of the consecration of the first woman bishop, Canon Joanna Penberthy, as Bishop of St Davids on 21 January.
In January 1997, 62 women were ordained, with their names set to feature on a new logo.
The services will take place at cathedrals in Llandaff in Cardiff, Newport, Bangor in Gwynedd, St Asaph in Denbighshire, Brecon in Powys and St Davids in Pembrokeshire.
Canon Enid Morgan was among the first ordained, along with Canon Penberthy, and she will give an address at Bangor Cathedral.
She described "frustration" after spending 12 years as a deacon, with a sense of "much energy wasted".
But then "things seemed to happen very quickly" after a bill was passed in September 1996 allowing women priests, she said.
Canon Morgan added: "A whole generation has grown up seeing women priests and their ministry as normal and we can start taking some things for granted."
The 20th anniversary of the ordination of Wales' first women priests will be celebrated with simultaneous services at every cathedral in the country.