Naismith joined the Toffees back in 2012, and he has learnt just how talented the centre-back is during that time.
The England international has played a key part in Everton's team for a number of seasons, and Naismith is glad to be on the same side as him.
"I think Jags is up there with one of the ones I probably underestimated before I joined Everton," Naismith said. "He’s not the biggest for a centre-half but he is phenomenal because of the power in his legs, how he covers the ground and how he reads the game.
"He’s decent with the ball at his feet as well; it’s not like he’s an old fashioned type of centre-half that just gets it and gives it, he’s calm and composed on the ball.
"On the other side, in the changing room, he is a great captain and he’s a lively guy that keeps the changing room going at low times."
Jagielka has been in great form for Everton this season, and despite his advancing years he is looking as sharp as ever.
The 33-year-old has been a rock at the heart of the Toffees' defence, and even though he has not had a settled partner yet this term, his performances have not been affected.
His consistent excellence has helped the Toffees to climb into seventh place in the Premier League table, with Roberto Martinez's men just two points adrift of the Champions League qualification spots.
Jagielka is currently on international duty with England, with the Three Lions due to play Euro 2016 qualifiers against Estonia and Lithuania in the coming week.