Lawson plays Emily Bennett on The CW's vampire series and also appeared as Kendra in three Buffy episodes between 1997 and 1998.
"Tonally, they feel like such different shows to me," the 33-year-old told myFanbase. "The Vampire Diaries feels a little more serious, whereas Buffy was more humorous and tongue-in-cheek, I think."
Lawson - who has appeared in a total of five Vampire Diaries episodes - added that her characters on each show were also "just so different".
"Emily is very internal and still... where Kendra was very physical, emotionally inexperienced and solid," she said.
The Vampire Diaries returns to The CW in the US for its fourth season on Thursday, October 11 at 8/7c. In the UK, season four is expected to air on ITV2 in late 2012.