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Alecto Carrow and Bellatrix Lestrange are the only known female Death Eaters.

NOTE: Narcissa Malfoy is NOT a Death Eater. Even though her husband, sister and son are Death Eaters, she is or was loyal to Lord Voldemort though.

In the begining of Deathly Hallows part 1 When Voldemort and the Death Eaters are having the meeting at Malfoy Manor, when Nagini slithers down the table she passes two people who appear to be female, whether they are Death Eaters or not is uknown.