The incident occurred when they were fitting window panes of the Shabari Park building, coming up opposite the RK Studios in Govandi suburb.
Suddenly they lost their balance and fell nearly 80 feet below, the Brihanmumbai Municipal Corporation official said.
Other workers rushed them to the Shatabdi Hospital where they were pronounced dead.
It is not clear if they were wearing safety belts or whether a safety net was installed below to prevent such accidents.