The Syrian Observatory for Human Rights said that in total 14 people had been executed for alleged adultery or homosexuality in the war-torn country since July, half of them women.
It released a video showing fighters from Al-Nusra Front, Al-Qaeda's Syrian affiliate, tying up a woman and shooting her in a square in the town of Maaret Masirin in the province of Idlib.
A crowd of civilians and fighters are seen watching, as a jihadist accuses the woman of "corrupting the earth, and adultery".
Islamic law views all sex outside marriage as a punishable crime.
Signup to our newsletter and follow us on Facebook and Twitter!
Other cases of execution documented by the Observatory include a man accused of adultery who was stoned to death by Al-Nusra Front and other Islamist groups in the town of Saraqeb in Idlib.
The rival Islamic State (IS) jihadist organisation is also accused of executing several women and men for alleged adultery or homosexuality.
Another Islamist group threw a man thought to be gay off a building in the northern province of Aleppo.
Observatory director Rami Abdel Rahman said that more executions might have taken place elsewhere in Syria that were not documented.
IS has captured large swathes of territory in Syria and Iraq, declaring a "caliphate" and imposing its harsh interpretation of Islamic sharia law.