A blast-proof window and mullion system for sustaining and mitigating an explosion and/or blast to the window and mullion system on a multi-storied building or structure. The window and mullion system includes a blast-resistant mullion having a mullion housing with mullion walls with outer surfaces; and a pressure bar member having a pressure bar housing with an interior wall and a pair of outer walls being connected to the interior wall to form a center channel opening. The outer walls are angled for reducing the space between the angled walls and for reducing the size of the center channel opening for reduction of bullet and/or blast penetration to the interior wall of the pressure bar member. Also, one of the mullion walls of the mullion housing includes a mullion tongue thereon having a pair of tongue extension arms for forming a vertical bolt receiving channel therebetween. Each of the tongue extension arms have interior serrated surfaces for receiving threaded bolts between the interior serrated surfaces. The interior wall of the pressure bar member has a pair of spaced-apart pressure bar extension arms thereon. The interior wall of the pressure bar member includes a plurality of spaced-apart bolt openings for receiving a plurality of the threaded bolts therein for permanently locking together the pressure bar extension arms with the mullion extension arms in order to join together and lock the pressure bar housing of the pressure bar member to said mullion housing of the blast-resistant mullion to form the blast-proof window and mullion system.