I attended Mass celebrated by a woman, is this valid?

No. If what you attended was presented as a Catholic Mass in which a woman attempted to consecrate the bread and wine, it was not valid.

The Catholic Church teaches definitively that only a validly ordained priest can confect the Eucharist. This is not a matter of discipline that can change; it concerns the sacrament itself.

The Code of Canon Law states clearly:

“Only a validly ordained priest can confect the sacrament of the Eucharist.” (Code of Canon Law, can. 900 §1)

This means that without a validly ordained priest, there is no consecration. No matter the intention, sincerity, or ceremony, the bread and wine do not become the Body and Blood of Christ.

The Church also teaches definitively that the Church has no authority to ordain women. In Ordinatio Sacerdotalis, Pope St. John Paul II wrote:

“Wherefore, in order that all doubt may be removed regarding a matter of great importance… I declare that the Church has no authority whatsoever to confer priestly ordination on women and that this judgment is to be definitively held by all the Church’s faithful.”
— John Paul II, Ordinatio Sacerdotalis (1994)

Therefore, a woman cannot be validly ordained a priest. And since only a validly ordained priest can consecrate the Eucharist, a woman cannot celebrate a valid Mass.

The Catechism of the Catholic Church also states:

“The minister of the Eucharist is a validly ordained priest (bishop or priest).” (CCC 1411)

What about a Communion service?

In some places, when no priest is available, a Communion service may be led by a deacon or even a layperson (including a woman). In that case, Holy Communion is distributed from hosts that were consecrated previously at a valid Mass. No consecration happens during that service.

So if you attended:

1. A Communion service led by a laywoman, where previously consecrated hosts were distributed — that is permitted in certain circumstances, and the Eucharist would be valid because it was consecrated earlier by a priest.
2. A ceremony in which a woman attempted to celebrate Mass and consecrate bread and wine — that was not valid. No Eucharist was confected.

The distinction is essential. A Communion service is not a Mass. On Good Friday, for example, the Church does not celebrate Mass. The hosts distributed were consecrated the previous day, on Holy Thursday.

If you truly witnessed someone attempting to simulate the Mass without valid ordination, especially publicly as a Catholic liturgy, this is a serious matter. It would be appropriate to inform the diocesan bishop so he can investigate and clarify the situation.

The Eucharist is not symbolic in Catholic teaching. It is the true Body and Blood of Christ. And because it is so sacred, the Church guards the sacrament carefully.

If you’d like, tell me exactly what happened — was it inside a Catholic parish? Was it advertised as a Mass? That will help clarify the situation more precisely.