The Britain-based watchdog added that at least 120 of those killed in the battle for one of the regime's last remaining bastions in the west of Aleppo province were army troops.
On Sunday alone, rebels killed more than 34 government troops in the facility.
After rebels battled troops for control of the sprawling eight-hectare complex, located some 11 kilometres (eight miles) west of Aleppo city, they combed the academy buildings on Sunday, said the Observatory.
Amateur video shot by Islamist rebels and distributed by the anti-regime Aleppo Media Centre showed a black flag flying over one of the academy buildings, while a large poster showing President Bashar al-Assad had been torn.
Another video showed rebels aboard a military vehicle captured from army hands and stashes of ammunition seized from the academy.
"This is the police academy, after it has been liberated," said an unidentified cameraman shooting an amateur video in the complex, which could not be immediately authenticated by AFP.
"I lost my brother and my best friend in this battle," a fighter identified only as Bilal told the cameraman.