The RBS 6 Nations champions host the world’s number two-ranked team at the Millennium Stadium on Saturday.
They lost to New Zealand twice in this season’s Rugby Championship but du Plessis insists the gap is closing and has fired a warning shot to Wales.
“We’re building towards something special,” said Bismarck.
“Heyneke Meyer is an exceptional coach. In our first season under him we did struggle to adapt to exactly what he wanted and we had people playing their first Tests. They now have 20, 22, 25 Tests.
“As a side we have become more mature, more clinical. We’re putting a few blocks together.
“A year ago Marcell Coetzee had zero Tests, Eben Etzebeth had zero Tests, Juandre Kruger had zero Tests.
“The All Blacks are the best team in the world but I wouldn’t count us out.”
Wales have not overcome South Africa since recording a 29-19 victory at the official opening of the Millennium Stadium in 1999, losing the next 13 matches.
But the last defeat came at the Rugby World Cup, where Wales lost by a single-point with Rhys Priestland missing a late drop-goal to win.
Du Plessis expects a formidable challenge from Warren Gatland’s men but is relishing a return to his favourite ground in world rugby.
“Cardiff will be good. I always love playing in Cardiff. The Millennium is my favourite stadium in the world.
“Wales are Six Nations champions, a lot of their players were in the Lions team. They’re going to be good.”
