The Britain-based group's director, Rami Abdel Rahman, said "January was among the bloodiest months since the beginning of the conflict" in March 2011.
Among the dead were 47,998 civilians, including more than 7,300 children.
The Observatory said the real toll could be much higher because of the extreme secrecy of rebels, jihadists and the regime about casualty figures.
The conflict began after a regime crackdown on peaceful anti-government demonstrations, sparking an armed uprising against President Bashar al-Assad.
In addition to the dead and a much larger number of wounded, millions of people have been displaced internally and as refugees.
There was no let-up in the bloodshed on Saturday, with at least 46 civilians killed by helicopter-borne barrel bombs dropped on the northern city of Aleppo, the Observatory said.
Abdel Rahman told AFP that among the victims were "33 civilians in the Tareq al-Bab area" alone.
At least another seven people died in a double car bombing carried out by the jihadist Islamic State of Iraq and the Levant targeting a rebel headquarters in Aleppo.
Moderate and Islamist opposition fighters have been battling ISIL since early January, after accusing the group of a spate of abuses against civilians and rebels.
Meanwhile, in the central province of Hama, the Observatory said at least 12 government fighters were killed around the town of Morek.
Deadly Lebanon car bombing
The group said rebels, including from the Al-Qaeda-linked Al-Nusra Front, had seized Morek overnight, cutting a strategic regime supply line from Hama city to two military bases in neighbouring Idlib province.
And in neighbouring Lebanon, a car bomb killed at least four people and wounded 15 at a petrol station in the eastern town of Hermel, a stronghold of the Shiite Muslim movement Hezbollah near the border, the army said.
Al-Nusra Front in Lebanon, named after its Syrian affiliate, claimed the attack on Twitter, saying the suicide bombing was a response to Hezbollah involvement in Syria.
The attack is the seventh targeting Hezbollah strongholds since the group said it had sent men to Syria to fight alongside Assad's forces against mainly Sunni rebels.
The United Nations urged Lebanon's feuding factions to refrain from getting involved in Syria's crisis following the car bomb.
The United Nations Security Council issued a statement condemning the "terrorist attack" and calling for the perpetrators to be brought to justice.
Council members also appealed to all Lebanese people "to preserve national unity in the face of attempts to undermine the country's stability" and for all parties to refrain from any involvement in the Syrian crisis.
In a separate statement the UN secretary general's spokesman Martin Nesirky said Ban Ki-moon also strongly condemned the car bombing and extended his condolences to the bereaved.
"The recent escalation in acts of terrorism and violence in Lebanon is of grave concern," he said, adding that Ban called on all players, including the army and security forces, "to confront such unacceptable and indiscriminate actions and to safeguard their country's security and stability".
On the diplomatic front, the two sides and world powers were assessing the 10 days of talks in Switzerland last month which showed few results, and with prospects of a follow-up meeting uncertain.
Diplomats said a UN Security Council resolution on the lack of access to Homs and other besieged cities could be ready this week.
Syrian Foreign Minister Walid Muallem was blunt after the final session Friday, saying "we have not reached tangible results".
Despite persistent pressure from UN-Arab League envoy Lakhdar Brahimi, and co-sponsors Russia and the United States, regime and rebel delegations failed to agree on a single point.
On Saturday, Muallem dismissed what he branded the "coalition of the so-called 'opposition'", and said it had been a "stain" on them that they had refused to sign a declaration condemning "terrorism" in Syria.
The regime had sought to focus discussions on "terrorism" -- its term for those seeking Assad's overthrow.
Muallem also took US Secretary of State John Kerry to task for insisting at the opening of the "Geneva II" conference that Assad "will not be part" of any transitional government.
And he repeated earlier assertions that his team would await guidance from Damascus before announcing whether it would attend further talks, tentatively set for February 10.