The 35-year-old actress is said to be waiting for responses from Jude Law, Meryl Streep, Marion Cottillard, Liev Schreiber, Naomi Watts and Ben Stiller. Meanwhile Ricky Gervais, Christina Aguilera, Demi Moore, Elijah Wood, Javier Bardem, Kevin Bacon and Julianne Moore have all agreed.
Each celeb will be photographed wearing a special hat and then will write down what their first words would be if they'd been unable to speak for years.
The pictures will then be put together to form a book called The Golden Hat, which was inspired by a poem written by an autistic boy called Keli Ericsdottir
Kate first met Keli in Iceland when she voiced a documentary titled A Mother's Courage: Talking Back To Autism, about his battle to communicate, and based her idea on his poem about an autistic boy who can communicate when he wears a magical hat.
The book will be released in November, with all proceeds going towards Kate's autism charity The Golden Hat Foundation.