A blind body braking mechanism used in a non-cord window blind assembly is disclosed to include two take-up wheels, two one-way clutch units respectively disposed adjacent to the two take-up wheels and respectively provide one clutch wheel, two guide rods respectively disposed at one lateral side relative to one respective take-up wheel in a parallel manner relative to the axis of the take-up wheels, and two transmission cords respectively extending over one respective guide rod and wound round one respective one-way clutch wheel with respective one end thereof fixedly connected to one respective one-way clutch wheel. Subject to the functioning of the guide rods, the transmission cords can be properly wound round the respective take-up wheels.