The mass was interrupted and those present called the emergency services to the church of Sant'Andrea in the northern Italian municipality of Zignago.
The priest was taken to the emergency room.
The police are now investigating whether the corrosive liquid got into the chalice through carelessness or deliberately.
The reception of communion is part of the Eucharistic celebration.
Prior to this, bread and wine become the body and blood of Christ in the consecration, thus changing their "substance".