AmateurSong was the 1999 U.S. Girls Junior champion. She won a total of 15 national junior tournaments from 1999-2001. In 2000, at the age of 13, Song tied for 10th in the Nabisco Championship and played the final round in the final pairing with Karrie Webb and Dottie Pepper. In August 2000, at the age of 14, she became the youngest player ever to advance to the semifinals of the U.S. Women's Amateur Championship. She finished 13th in the 2000 Safeway LPGA Golf Championship. She was also named the 2000 Golf Digest and GolfWeek Girls Junior Player of the Year and American Junior Golf Association (AJGA) Player of the Year. In 2001, Song played in her second Kraft Nabisco Championship, where she tied for 46th. Song was the recipient of the 2001 Nancy Lopez Award, which is presented to the best female amateur golfer of the year. In 2002, she won the Harder Hall Invitational by eight shots and also finished fifth in the South Atlantic Ladies Amateur and tied for 30th at her third consecutive Kraft Nabisco Championship. She tied for 51st at the 2002 U.S. Women's Open, earning low-amateur honors. Song participated in the 2002 World Amateur Team Championships in Malaysia, placed first individually and helped the Thailand team to their second-place finish. She was the co-medalist for the second consecutive year at the 2002 Futures Tour Qualifying School and the same year was named Golfweek's Female Amateur of the Year. In January 2003, she defended her title at the Harder Hall Invitational, won the& South Atlantic Ladies Amateur and tied for 21st in her fourth consecutive Kraft Nabisco Championship. At the 2003 U.S. Women's Open, she was paired in the second-to-last group with Annika Sorenstam and finished fifth. Song was the stroke-play medalist at the U.S. Women's Amateur Championship and advanced to the quarterfinals in match play. Song was the top-ranked female amateur from 2002-03. She made six out of six cuts as an amateur in LPGA major championships and finished in the top 10 twice. She turned professional in August 2003, and after receiving permission from then-LPGA Commissioner Ty Votaw to receive an age exemption, she applied to the LPGA Final Qualifying Tournament.