Though the idea may seem preposterous to some, the question seems to stem from the remote possibility that Hitler's grandfather was Jewish. Hitler's father, Alois, was registered as an illegitimate child with no father when born in 1837 and to this day Hitler's paternal grandfather is unknown. Alois' mother, Maria Schicklgruber, is known to have worked in the home of a wealthy Jew, so there is some chance, however small, that a son in that household got Hitler's grandmother pregnant.
In 1933, the London Daily Mirror published a picture of a gravestone in a Jewish cemetery in Bucharest inscribed with some Hebrew characters and the name Adolf Hitler but it is now known tha this Bucharest Hitler could not have been the Nazi leaders grandfather. At the time, though, this picture sufficiently worried Hitler that he had the Nazi law defining Jewishness written to exclude Jesus Christ and himself.
In 2010, the British paper The Daily Telegraph reported that a study had been conducted in which saliva samples were collected from 39 of Hitler's known relatives to test their DNA origins and found, though inconclusively, that Hitler may have Jewish origins. The paper reported: "A chromosome called Haplogroup E1b1b1 which showed up in [the Hitler] samples is rare in Western Europe and is most commonly found in the Berbers of Morocco, Algeria and Tunisia, as well as among Ashkenazi and Sephardic Jews ... Haplogroup E1b1b1, which accounts for approximately 18 to 20 per cent of Ashkenazi and 8.6 per cent to 30 per cent of Sephardic Y-chromosomes, appears to be one of the major founding lineages of the Jewish population." Again, this study, though scientific by nature, is inconclusive.
Similar "allegations" of Jewish ancestry have been levied against Iranian leader Mahmoud Ahmadinejad who regularly claims that the Holocaust never happened.
Despite the claims, Adolf Hitler was not Jewish.