The 'Not Fair' star wrote on her Twitter page that the Scottish singer was "so overrated", though she conceded in French that the same could also be said of her.
Allen said: "Susan Boyle is so overrated. Je suis overrated aussi."
When challenged by her Twitter followers, she replied: "I'm allowed to have an opinion. I thought her timing was off, no control, and I don't think she has an amazing voice.
"Yes, she can sing, but it's not about talent with her, is it? She seems like a lovely lady but if its about talent, that Shaheen kid should win."
She added: "I have never in my life claimed to be talented. I do work hard at writing songs and putting on entertaining concerts though."
Allen also said that the show is "verging on child cruelty" with the treatment of "that poor little Natalie girl" and claimed that her "goddaughter aged four was in a hysterical fit of tears" watching the programme.