Thank you for contacting BibleAsk.
The Catholic Church may conduct a mass on Saturday, however, their official day of worship is Sunday. Here are some quotes from their literature:
“Sunday is a Catholic institution, and its claims to observance can be defended only on Catholic principle… From beginning to end of Scripture there is not a single passage that warrants the transfer of weekly public worship from the last day of the week to the first.” –The Catholic Press, Sydney, Australia, August, 1900.
“Ques. – Have you any other way of proving that the (Catholic) Church has power to institute festivals of precept (to command holy days)?”
“Ans. – Had she not such power, she could not have done that in which all modern religionists agree with her: she could not have substituted the observance of Sunday the first day of the week, for the observance of Saturday the seventh day of the week, a change for which there is no Scriptural authority.” – Stephan Keenan, A Doctrinal Catechism, page 176.
“Perhaps the boldest thing, the most revolutionary change the Church ever did, happened [when] the holy day, the Sabbath, was changed from Saturday to Sunday. ‘The Day of the Lord’ (dies Dominica) was chosen, not from any directions noted in the Scriptures, but from the Church’s sense of its own power”- Sentinel, Saint Catherine Catholic Church, Algonac, Michigan, Volume 50, Number 22, May 21, 1995
The Bible is clear on the fact that we should observe the seventh day Saturday (Genesis 2:2,3; Exodus 20:8-11), where as the Catholic Church promotes Sunday. God’s true church will not contradict the Bible “Here is the patience of the saints; here are those[a] who keep the commandments of God and the faith of Jesus“ (Revelation 14:12).
There are several other doctrines that the Catholic church and the Seventh Day Adventist church hold with differing views such as the authority of Bible, the state of the dead, prophecy, ministry of priests, Hell, heaven, saints as well as others.
In His service,
The BibleAsk Team