Several people were also wounded in the attack that targeted the market in the Halak neighbourhood in northeastern Aleppo, the Britain-based monitor said.
Rebel-held areas of Aleppo have come under massive air assault since mid-December as government forces try to regain full control of Syria's second city and one-time commercial hub.
"A Syrian fighter jet fired a missile at the (Halak) neighbourhood, and within minutes it fired another," Observatory head Rami Abdel Rahman told AFP.
Activists posted a YouTube video showing an ambulance trying to make its way across rubble to the site and the facades of buildings badly damaged.
Youths are seen carrying the body of a man in a rug as others dig through rubble for victims.
The authenticity of the video could not be immediately verified.
Today's air raids come a day after the Observatory reported that twin air strikes on a school in the Ansari neighbourhood controlled by insurgents killed 18 people, 10 of them children.
The Observatory, which relies on activists and medics on the ground for its reports on the three-year war in Syria, said that at least one teacher was also among the dead in yesterday's strikes.
Rebel bombardments of regime-held areas of Aleppo have also intensified in the past few weeks.
On Sunday, rebels fired mortar rounds into parts of the Old City where government forces are entrenched and into other areas of Aleppo, killing more than 20 people.
Regime forces have also stepped up the use of barrel bombs dropped by helicopter on rebel positions in recent weeks, according to the Observatory.