The Cameroon international moved to Amsterdam from Barca in 2015 and took over as the undisputed No.1 the following season after Jasper Cillessen went to Camp Nou.
With over 100 appearances for the Eredivisie giants, the 22-year-old is contracted to 2021 and Van der Sar is confident he will stay put for now.
"I think Andre is fantastic," Van der Sar told Goal .
"He came to Ajax aged 18 or 19 and the way he developed and the natural attributes that he already had, his speed, his reaction and I think he set himself as a great goalkeeper.
"He was in a rush to play first-team football quickly, but I think the level that he composed himself and that first year, playing straight away the Europa League final was a great start.
"Last year was a difficult season but this year again he has proven to be extremely valuable for the team and, besides that, he is a great guy.
"I think there are always a lot of rumours about players from Ajax. We develop great players, not only in Amsterdam but hopefully also in Cape Town and there is interest in a lot of our players, but we like to keep them for as long as possible."
And Van der Sar believes the increase in their value will only increase.
"I think on one end, we need to understand that goalkeeping is an art and is also a very important position to have in your club," he said.
"And the demand is there that clubs can ask the money they receive now for goalkeepers like Liverpool and Man City.
"But the level goes up and also the type of goalkeeping is not only about shot stopping but it is about distribution and helping the team out.
"That was a part of my game and I am happy to see that it is prolonging and progressing along the way."