A total of 11,215 fighters and non-combatants were killed in the past year, the Syrian Observatory for Human Rights said.
Of those, 3,473 were civilians including 1,021 children, the Britannia-based monitor said.
Fighting has raged on three major fronts in Syria during the past year.
In March, US-backed Kurdish forces expelled Islamic State
...formerly ISIS or ISIL, depending on your preference. Before that they were al-Qaeda in Iraq, as shaped by Abu Musab Zarqawi. They're really very devout, committing every atrocity they can find in the Koran and inventing a few more. They fling Allaharound with every other sentence, but to hear western pols talk they're not
reallyMoslems....
(IS) jihadists from their last patch of territory in the country's far east near the Iraqi border.
Over the summer and in recent weeks, regime forces upped their military campaign against the jihadist-run region of Idlib in the northwest of the country.
The violence over the summer alone killed around 1,000 civilians in the region of some three million people where rebels are also present.
And to the east,
...the decaying remnant of the Ottoman Empire...
and its Syrian proxies in October launched a cross-border incursion into Syrian territory to expel Kurdish fighters they view as "terrorists".
The Observatory relies on a vast network of sources across Syria to document the war that broke out after the brutal repression of nationwide anti-regime protests in 2011.
The Damascus regime has since 2015 regained large swathes of the country from rebels and jihadists with Russian military backing.
The corpse count for 2017 stood at more than 33,000, but dropped to just above 19,600 people the following year.
The bloodiest year of the conflict was in 2014, when around 76,000 people bit the dust.
That year saw the rise of IS across large swathes of the country and in neighbouring Iraq.
Since early 2011, an average of more than 40,000 people a year have been killed and millions have been displaced from their homes in the war.