The mortar shell landed at the inner gate of the fairgrounds south of Damascus near the international road of the airport, Xinhua news agency reported.
The wounded were transported to a hospital in Jaramana area near the fairgrounds and later to the Mujtahid hospital in Damascus. A paramedic said all of the victims were civilians.
The attack on Sunday highlighted the security instability near the capital.
Last week, the Syrian government held the International Damascus Fair, the country's famous trade fair, for the first time since 2011.
The state media said companies from 43 countries took part in the fair.
The government aimed to send a message that the country's economy was being revived with the victory of the Syrian Army on the ground.
The turnout at the Damascus fair was huge and unexpected. On August 18, around 8,00,000 people thronged the fairground, causing suffocation in traffic on the airport road.
The mortar shell, fired by rebels in eastern Damascus, apparently aimed to send a message that the rebels were still capable of undermining the security in the capital.
Although no party has claimed responsibility for the attack, it is most likely to have been fired by the Al Qaeda-linked Nusra Front, otherwise known as the Levant Liberation Committee.
The 10-day fair was seen by the residents of Damascus as the beginning of the return of normalcy to their lives. In pre-war times, the Damascus fair used to be a high-profile event.
Established in 1954, the fair's last edition was held in 2011, the first year of the Syrian war.
In later years, the fair was suspended because of the battles, particularly those around the fairgrounds in southeastern rim of Damascus.
The fair showcases all kinds of products including Syria-assembled cars, electronics, food items and construction gears. Syria-based foreign embassies also have pavilions in the fair.
Foreign investments will also play a role in shoring up the sluggish economy in Syria, which took a heavy beating during the war, Xinhua reported.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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