Mosteller won the crown Saturday night at the pageant in Columbia. The 23-year-old from Mount Pleasant is a Furman University graduate and is attending the University of South Carolina's law school.
Mosteller sang "Being Alive," from the 1970s musical "Company" for her talent. She was a preliminary swimsuit winner.
Mosteller will talk about her plans as Miss South Carolina for the next year at a Sunday morning news conference.
The runner-up was Miss Greenville County, Lindley Mayer. Third place went to Miss Spartanburg, Clarka Wickliffe, fourth place was Miss Hilton Head Island, Lauren Cabaniss, and fifth place went to Miss Greater Greer, Lanie Hudson.
Miss Mauldin Teen, Brook Sill, won the Miss South Carolina Teen crown.