Lohan explained that she is endorsing the Republican candidate because she is worried about jobs, E! Online reports.
"I just think employment is really important right now," she said. "So as of now, Mitt Romney. As of now."
However, Lohan didn't elaborate on her reasons for backing Romney, saying: "It's a long story."
Romney's other celebrity supporters include Stacey Dash, Clint Eastwood and Jon Voight, while President Barack Obama counts Katy Perry, Jay-Z and Scarlett Johansson among his famous backers.
Lohan is currently the centre of fresh controversy after allegedly being involved in a violent argument with her mother Dina Lohan and telling her father Michael Lohan on the phone that her mum was high on cocaine.
She has since claimed that she was lying and criticised her father for making the call public.
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