The 10-year-old pop star - who is the daughter of Will Smith and Jada Pinkett-Smith - is signed to the rapper's Roc Nation record label but when they first sat down to discuss her career the young singer nodded off.
She said: "When I met with him (Jay-Z) in Japan I was so tired because I was hanging out the night before and had been dancing and having fun and I didn't know we had to meet Jay-Z that next morning so I went to sleep at, like, 4am and I fell asleep in the meeting!"
But the 'Whip My Hair' singer insists she didn't miss anything important, and was able to pretend she was awake because she was wearing dark glasses.
She added in an interview with UK station BBC Radio 1: "I had glasses and so I was, like, nodding along, but they were listening to the song and he was just talking to my mom and dad. But I was really tired. I was probably asleep for, like, 10 minutes of it. But I didn't miss anything (really good), that's the cool part I only missed the parts where he was explaining to my mom and dad where we're gonna be going and when we were gonna drop the single, stuff like that - although I guess that's important. But we got to hear all the songs they had for me, we have a lot of bombs to drop. It's gonna be like 'boom'."
Willow admits she sleeps a lot and relies on her brother Jaden - who has starred in several movies, including 'The Karate Kid' - to be her alarm clock.
She said: "I sleep until someone screams at me. It's usually my brother, mostly."