St. John the Baptist Cathedral (Slovak: Katedrála svätého Jána Krstiteľa, Hungarian: Keresztelő Szent János székesegyház)[1] is one of the most significant historic monuments of Trnava, western Slovakia.

The donor of this Cathedral, Miklós Eszterházy, entrusted its construction to the Italian masters Antonio and Pietro Spazzi in 1629.

Above its main portal there is a shield with figures of seated angels and the stoned crest of the Esterházy family.

The painters and stuccoer's decoration of the interior is the work of artists G. B. Rossa, G. Tornini and P. Conti.

In December 1978 Pope John Paul II established the church as the Cathedral of the Archdiocese of Trnava.