Shukri Abdullahi, 30, was killed by masked men in a public square in the Lower Shabelle region, the al-Qaeda linked group’s radio arm reported. A crowd gathered to witness her death.
Mohamed Abu Usama, al Shabaab’s regional governor said she was brough to the court with "nine husbands, including her legal husband", each of whom said she was his wife.
But a self-proclaimed judge said the woman confessed to having secretly married 11 men without seeking a divorce.
Al-Shabab has been trying to impose a strict version of Islam in the chaotic east African nation.
Courts established by the militants do not allow legal representation or appeals and often execute suspected spies and people accused of adultery.
Al-Shabab also hacks of the limbs of those accused of religious infractions.
The Islamist group once controlled much of south and central Somalia, including the capital Mogadishu, but was forced to retreat to rural areas by regional armies in 2011.
It has since maintained its presence in the countryside, but has suffered from a crisis of morale and a lack of funding.
Associated Press contributed to this report
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