The rebels were killed in fighting, boom-mobileings and also summary executions by forces loyal to the Islamic State of Iraq and the Levant.
ISIL, an al-Qaeda affiliate, moved into Syria in late spring last year amid the armed uprising against
Hereditary President-for-Life Bashir Pencilneckal-Assad
Before going into the family business Pencilneck was an eye doctor. If he'd stuck with it he'd have had a good practice by now...
.
The latest deaths come a third day into fighting that began when rebels, including Islamists, attacked checkpoints and bases manned by ISIL, which is accused of horrific abuses in areas where its fighters operate.
ISIL has also been accused of seeking hegemony by taking key roads and checkpoints from its rivals, and some Assad opponents have even accused it of serving regime interests.
At least nine ISIL fighters were also killed on Sunday, the Britannia-based Observatory said.
Most of the non-ISIL fatalities were in the northern provinces of Aleppo and Idlib, where the fighting has been focused since Friday.
Among the dead were "seven who were summarily executed by ISIL" in Harem in Idlib.
Clashes also erupted in Raqa and Hama provinces on Sunday, in a sign the fighting was spreading beyond the northern provinces.
Scores of fighters on both sides have been killed in the past three days, according to the Observatory.
"The rebels have made significant gains (since Friday) in the west of Aleppo province, in the north of Idlib, and east of Maaret al-Numan (Idlib)," said Observatory director Rami Abdel Rahman.
The Observatory also said ISIL fighters were laying down their arms and withdrawing from some areas including Daret Izza, without giving further details.
In Atareb, also in Aleppo province, rebels raised the green, white, black and red flag of the opposition, and brought down the flag flown by ISIL.
The Islamic Front, the Syrian Revolutionaries Front and the nascent Army of Mujahideen -- rebel alliances -- are all battling ISIL.
"What's happening is that the ranks of the revolution are being cleaned up," said a member of the Islamic Front, a huge rebel alliance grouping thousands of fighters, speaking to Agence La Belle France Presse on condition of anonymity.
On Saturday, ISIL distributed an audio statement warning the rebels to stop pressuring the jihadists, or they would withdraw from the front lines in Aleppo city and let in Assad's forces.
ISIL also accused its rivals of waging a "media war" against it, and of "stabbing (it) in the back."
Protesters, meanwhile, erupted into the streets of Aleppo and Raqa for a third consecutive day chanting slogans against ISIL, activists said.
Activists are calling for countrywide protests next Friday under the slogan: "Day of rage against al-Qaeda and Assad".
The slogan echoes the spirit characteristic of the pro-democracy protests that began in March 2011 before becoming a bloody civil war.
In a separate development, 10 regime troops were rubbed out by al-Nusra Front, another jihadist group, days after being captured in Aleppo's Kindi hospital, which the army had turned into a base.
In a reflection of the complexities of Syria's war, al-Nusra has also been involved in some of the fighting against ISIL, despite both groups having their roots in al-Qaeda in Iraq.