A mower blade assembly (10) includes an elongated blade bar (11) having two oppositely disposed cutting ends (13). A pair of removable bottom blades (22) and a pair of removable top blades (23) are removably mounted to the blade bar. The bottom blade has two oppositely disposed serrated cutting edges (27) so that either of the two cutting edges may be utilized for cutting purposes. Each top blade has a forward portion (31) which includes a series of blade segments (32) with serrated cutting edges (33) and a series of mulching blades (34) with serrated cutting edges (35). The top blade also has an elongated rear portion (37) that is oriented at an angle with respect to the cutting blades and blade bar. The angle of the rear portion creates or defines an airfoil deflector which increases the vacuum effect of the rotating blades.