It was confirmed last night that the 63-year-old Sarah Jane Adventures star had died after battling cancer.
Smith, whose second series of Doctor Who is due to begin this Saturday, appeared alongside Sladen in the fourth run of the CBBC spinoff show.
"What struck me about Lis was her grace," Smith said. "She welcomed me, educated me, and delighted me with her tales and adventures on Doctor Who.
"And she also seemed to have a quality of youth that not many people retain as they go through life. Her grace and kindness will stay with me because she had such qualities in abundance and shared them freely."
He continued: "I will miss her, as will the world of Doctor Who and all the Doctors that had the good pleasure to work with Lis Sladen and travel the universe with Sarah Jane."
Smith joins showrunner Steven Moffat, Sarah Jane Adventures creator Russell T Davies and former co-stars including John Barrowman and Nicola Bryant in paying tribute to the much-loved actress.
> Obituary: Elisabeth Sladen
> Gallery: Elisabeth Sladen 1948-2011
> Reaction: Elisabeth Sladen 1948-2011
> Read our 2006 interview with Elisabeth Sladen
> Read our 2008 interview with Elisabeth Sladen
> Read our 2009 interview with Elisabeth Sladen