When she is due to give birth or what the babies' genders are were not immediately announced.
Grammer, 56, has four other children from previous relationships.
The twins will be his first children with 30-year-old flight attendant Kayte, whom he married in February 2011 shortly after divorcing Camille, his wife of 14 years.
"I am really looking forward to meeting these arrivals," UsMagazine.com quoted Grammer as saying of the twins after he won the Golden Globe Award for Best Actor in a TV Drama Sunday night for his work in "Boss."
Grammer is best known for his work on the sitcoms "Frasier" and "Cheers."