The church union in the Eparchy of Przemyśl-Sambor at the time of Bishop Prokop Chmielewski (1652–1664) is a neglected page of the historiography. There is no evidence to indicate parts of the diocese where Unites lived, as well as, the number of the churches is unknown, there is also no information about the Uniate priests involved in various levels of the hierarchy. The reign of bishop Chmielewski fall on difficult period of dual power in the eparchy of the Przemyśl-Sambor the Eastern Church. Simultaneous existence of the bishops of the Orthodox and Uniate denomination meant that they competed for the same cathedral, churches and worshippers. This was due to the complicated internal situation of Poland, involved in a civil war with the Cossacks, then in the war with Russia. The aggressors fought the church union in the name of the Eastern Orthodox Church, interfering in the internal affairs of Poland. This influenced the policy of King Jan Kazimierz towards the Church Union and the Orthodox Church. As the cathedral in Przemyśl was occupied by the Orthodox, the Uniate bishop Prokop Chmielewski resided in Walawa. He tried to maintain a semblance of hierarchical structure, thus, he called cathedral kryłos. He exercised jurisdiction over decanate of Krosno, Leżajsk, Muszyna and Oleszyce. Unites were the most represented in the royal estates, particularly in the district of Krosno, as well as, in the noble goods belonging to the Families of Fredro, Korniakta, Krasicki, Lubomirski, Sieniawski and Zamoyski. These are initial findings on the Uniate Church in the days of bishop Chmielewski. This matter requires further detailed research.