Early Christians honored the Sabbath on Saturday, the seventh day, and met again on Sunday (the "eighth" day, see Acts 20:7), to partake of the sacrament and celebrate Christ's resurrection. Later Paul de-emphasized the need to follow many Jewish laws/traditions. Eventually, Sunday became the Christian Sabbath.
A few Christian sects, notably the Seventh-Day Adventists, currently honor the Sabbath on Saturday, but most use Sunday.