The grounds for the decision were not immediately available following the announcement of the acquittals.
Faruq Lashin, former director of security in the Nile Delta province of Qalubiya north of Cairo, was among the four who had been charged with murdering demonstrators.
The prosecution inquiry had said the four accused tried to prevent protesters from taking part in a key day of demonstrations, the so-called “Friday of Anger,” the climax of four days of protests on January 28 last year.
Twenty-seven people were killed and 40 wounded in clashes on that day, one of the deadliest 24-hour periods in the 18-day uprising which saw some 850 people die.
The mass protests against the Mubarak regime were fuelled by anger against police brutality.
The fallen strongman and his one-time interior minister Habib al-Adly were both convicted on June 2 this year for their roles in the deaths of demonstrators and sentenced to life in prison.