Abstract: A glass block installation tool for preventing glass block from falling out of a window frame during installation. The glass block installation tool includes an elongate tubular sleeve. An elongate arm member has a first flange coupled to one end thereof that is adapted for engaging a window sill. The other end of the first arm member is telescopically inserted in the sleeve. The sleeve is positionable along the arm member. An adjustment member has a second flange extending from an outer end thereof and adapted for engaging a window sill. The adjustment member is threaded from a second end thereof towards the second flange. The second end of the adjustment member is slidably insertable in the sleeve opposite the arm member. A nut threadably engages the adjustment member and is positioned between the sleeve and the second flange.