Mueed Juma, 28, from the village of Musherifa in the Wadi Ara region in northern Israel, is believed to have entered Syria from Turkey several weeks ago, Israel Radio reported.
His family received notice of his death Tuesday along with a photo of his bullet-riddled body, Ynetnews.com said. Juma flew abroad with friends several weeks ago and had not been in contact with his family since.
There was no mention of the location where Juma was killed.
"We never thought he would think of entering Syria to fight alongside rebels against Assad," a member of his family told Ynetnews.com. "I hope the two others who are missing will return to their families safe and sound."
"He died a hero's death, fighting against the regime of Assad the criminal in Syria," The Jerusalem Post quoted another family member saying.
Ten Israeli Arabs are believed to have entered Syria to fight alongside rebel forces, Ynetnews.com said.