The 37-year-old - who is mom to daughter North West, son Saint West, and daughter Chicago West, who was carried via surrogate - graduated in 1998 from the Catholic, all-girls private school in Bel-Air.
"So my friends are anxious that we're going to run into people that they were mean to", she said.
She then shares a few selfies with groups of friends, including one in a classroom, before showing off the chemistry lab, where she explains 'this is where chemistry was back in the day; this is where I did really badly in this chemistry class'.
The mother-of-three donned a stylish white mini-dress for the occasion.
Glad Kim K had a good time looking back, though! As she was making her way into the school, she said: "We are walking down the same halls that we walked 20 years ago, this is insane!"
In her first video Kiki tells fans on Snapchat, "Of course, I had to get a party bus for the class of '98", adding, "and all my yearbooks waiting".
Kim Kardashian had lately been posting several pictures of herself in a bikini, on social media.
BTW, Kim wore her name tag and probably made the night by finally validating everyone's stories over the years that they "Went to school with Kim Kardashian".
For her, she dressed down for the affair, wearing a white button-down shirt, and her hair long and straight.