"My forever Valentine," the 61-year-old model wrote alongside a romantic black and white image of the two kissing. She added the hashtags, "#BowieForever" and "#ValentinesDay."
Bowie was 69 when he died last January of cancer.
Iman told "Good Morning America" in September that she was "holding up" in the months after his death. She said she planned to wear a "David" necklace every day in his honor.
"I’m wearing this until my death," she said.
The couple was married for 24 years and have one child together, daughter Alexandria “Lexi” Zahra Jones.
On Sunday, the rocker was awarded five posthumous Grammys for his final album, "Blackstar."
Iman celebrated his wins on Instagram. "Thank you for your love & support! BLACKSTAR WINS ALL FIVE NOMINATED GRAMMYS," she wrote.