How do Seventh-day Adventists differ from other Protestants?

Most noticeably is their observance of Saturday, not Sunday, as the Sabbath. But they also differ from many (but not all) Protestants in their teaching concering the nature of man, the state of the dead, and the manner of Christ's second coming.

Seventh-day Adventists claim that they are no inventors of new doctrines but recoverers of old truths--truths long eclipsed by the infiltration of pagan traditions and superstitions into the Christian Church.

Why Do Seventh-day Adventists observe Saturday as their day of rest?

Because God, in the beginning, set apart the seventh day of creation week as a perpetual memorial of His creative power. Saturday is the seventh day of the week. Sunday is the first day of the week.

In Exodus 20:8-11, it is written, "Remember the Sabbath day, to keep it holy. Six days shalt thou labor, and do all thy work: but the seventh day is the Sabbath of the Lord thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, not thy maidservant, nor thy cattle, nor the stranger that is within thy gates: for in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the Sabbath day, and hallowed it."

It is distinctly stated of Christ that it was His "custom" to attend the synagogue on "the Sabbath day" (Luke 4:16). And after His crucifixion, His closest disciples were so loyal to His teaching and example they would not even embalm His body on the holy seventh day. Instead, "they . . . rested the Sabbath day, according to the commandment"(Luke 23:56).

As Seventh-day Adventists have never been able to find a single text in the Bible suggesting that Christ authorized a change of the Sabbath from the seventh day of the week to the first, they say, "What else can a true Christian do but follow the clear teaching of the Word?"

How do Seventh-day Adventists know Saturday is the Seventh Day?

By the calendar. Every calendar shows Saturday as the seventh day of the week. Two unquestionable pieces of evidence confirm this: First, the fact that Orthodox Jews, from time immemorial, have observed the seventh-day Sabbath on Saturday; and, second, millions of Christians, for many centuries, have observed Sunday because Christ rose on the first day of the week.

Quoted from Arthur S. Maxwell, Religions in America

Note: The Seventh-day Adventists originally worshipped on Sunday. They were introduced to the Sabbath by the Seventh-day Baptists. Also, there are Seventh-day Churches of God--and of course, the Jews worship on Saturday (the Sabbath).