According to reports, the slain soldier has been identified as 20-year-old Abbas Medlej, a Shiite Muslim. His execution video was posted online by the ISIS members.
The Lebanese army is yet to confirm the authenticity of the gory video, but, the decapitated soldier's mother told a news agency that the pictures look real.
The ISIS militants, in a statement, justified his beheading by claiming that Medlej was killed because he was trying to escape and also fired on the captors.
"Yes, we slaughtered Lebanese soldier Abbas Medlej because he attempted to escape," the ISIS leader told Turkish news agency Anadolu.
The ISIS commander also claimed that "on the pretext of going to bathroom, Medlej fired shots at ISIS members."
Few days back, the ISIS militants had beheaded another Lebanese soldier and Medlej's colleague Ali Sayyed.
Last month, ISIS had captured dozens of Lebanese soldiers when they had raided Arsal town of the country.
After Iraq and Syria, ISIS has moved over to Lebanon, furthering its expansion.