The 28-year-old joined the Brazilians from Platinum Stars in 2009 and has slowly cemented his place as first-choice keeper, edging out Brian Baloyi and Calvin Marlin as the top dogs in Tshwane.
"I'm over the moon with the contract extension," Sandilands told the club's official website.
"It's been a dream come true for me to play for such a wonderful team like Mamelodi Sundowns and now I'm really glad that I get to play for the club a little bit longer.
"I'm thankful for the opportunity and hopefully I can contribute to the success of the team.
"We look to get a positive result against Kaizer Chiefs. It's going to be tough but we are determined to do well in order stay in a good position on the log."
Sandilands will get another chance to impress when the team travel to Soweto to take on Kaizer Chiefs in the PSL on Wednesday evening.