Saqlain has been with the club since 1997 and has featured heavily in their success during that period.
The 25-year-old off-spinner captured 53 wickets at an average 25.64 last season.
He has taken 183 Test wickets in 43 matches for Pakistan and 271 victims in 156 one-day internationals.
All rounder Azhar, 27, topped Surrey's bowling averages with 20 wickets at 17.25 in his first year at The Oval last season.
He also recorded the season's best figures of 8-61 against Lancashire.
"Saqlain has been an integral member of the team in the last five years and has been instrumental in our recent success," said cricket manager Keith Medlycott.
"Azhar made a big impression on the side during his short spell at the start of last season.
"He fitted straight into the team and I am extremely pleased that we have signed him on a two-year contract."
Promising young fast bowler Tim Murtagh has commited himself to Surrey for another three years.
The 21-year-old played for England in the under-19s World Cup two years ago and has been tipped for future international honours.
Fast bowler Phil Sampson, 22, has signed a two-year deal with the club and all-rounder James Benning has joined after signing a two-year contract.