The highest toll was in Douma, the largest town in the Eastern Ghouta region, where raids killed 22 civilians including at least two children, it said.
An AFP correspondent at the town hospital said he saw many wounded people, their faces bloodied. All the facility's beds were occupied by men, women and children.
A child burst into tears when he found his father in the hospital, the correspondent said.
Five more civilians were killed in the town of Sabqa and one in the town of Harasta, both also in Eastern Ghouta, the Observatory said.
The Eastern Ghouta region is adjacent to the capital's eastern neighbourhood of Jobar, which is divided between regime and rebel control.
Last month, the armed opposition launched a surprise assault against regime forces from Jobar, but was repelled after a week of fighting.
Eastern Ghouta has been under a devastating government siege since 2012, and is targeted regularly by air strikes and artillery.
It is the last remaining opposition stronghold near Damascus, where a string of local "reconciliation deals" have seen villages and towns brought back under the control of President Bashar al-Assad's government.
The regime is fighting to push rebels out of five neighbourhoods in Damascus.
The rebels control almost all of Qabun and Tishreen in the northeast, as well as half of Jobar in the east.
They are also present in Barzeh in the north and Tadamun in the south, but the neighbourhoods are covered by a truce with the regime.
More than 320,000 people have been killed and millions displaced since Syria's war started in 2011 with the brutal repression of anti-government protests.