DeGeneres (left) has been a vocal campaigner against Proposition 8
US talk show host Ellen DeGeneres has said she is "saddened" by the passing of a constitutional amendment banning same-sex marriage in California.
The amendment states: "Only marriage between a man and a woman is valid or recognised in California."
DeGeneres said America "had taken a giant step toward equality" by electing Barack Obama, but with the Proposition 8 amendment "took a giant step away".
Star Trek actor George Takei also said the evening was "bitter-sweet".
The 71-year-old, who wed his partner Brad Altman in September, said it was "astounding to think the hard-won equality" that enabled his marriage to take place "would no longer be possible for others".
Takei and Altman were among the first couples to receive a marriage licence when California began issuing them to gay couples in June.
The ruling puts in jeopardy thousands of same-sex marriages that have taken place in California since May.
Legal challenges to the measure, known as Proposition 8, are likely.
DeGeneres, who wed her partner, actress Portia Rossi, in August, bought $100,000 of TV airtime to campaign against the referendum.
The 50-year-old star said she would "continue to speak out for equality for all of us".