In a post to celebrate the occasion, The West Wing star, 58, gushed over Berkoff, 61, by sharing a picture of her on Instagram and penning a sweet note to her in the caption.
"Happy 31st Anniversary, baby," he wrote on Friday. "Your love has made my world. You are as beautiful, knowledgeable, fascinating, kind, and hilarious as you were so many glorious years ago."
"Partners in love for life!!" he added.
Lowe and Berkoff have been married since 1991. They first met when the two worked together on Rob's 1990 erotic thriller, Bad Influence. The pair share two sons, Matthew Edward Lowe, 29, and John Owen Lowe, 27.
In June, Rob also paid a sweet tribute to the jewelry designer in honor of her 61st birthday. Sharing a beautiful picture of Berkoff via Instagram, he wrote in the caption, "Happy Birthday to the love of my life."
"You are the whole package, and I am blessed," he continued. "Here's to many more years of love and fun! Xoxo."
Pascal Le Segretain/Getty
Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.
Earlier this year, the 9-1-1: Lone Star actor opened up to PEOPLE about seeing something truly special in Berkoff since the start of their relationship.
"I had the feeling that if I was ever going to be able to make it work with anybody, it was Sheryl," Lowe said as he recalled feeling "seen" for the first time in his life.
The actor also shared during the interview that he remained forever grateful that Berkoff took a chance on him.
RELATED: Rob Lowe Says His Family Is "The Thing I'm Most Proud Of"
"She saw things in me that nobody had ever seen before," he said at the time before calling his marriage to Berkoff one of life's greatest "miracles."
"I still think she's the hottest, sexiest, most beautiful, insane, complicated, entertaining person that I know, in addition to being a great mother," he added of his wife.