Abstract: A scaffold stabilizer for use on a scaffold platform, consisting of a multiplicity of longitudinal planks of uniform thickness assembled in side-by-side contact to form a supporting floor or platform for workers. The stabilizer comprises a generally C-shaped unitary metallic clamping member comprising upper and lower plate members rigidly connected to an end plate member, the upper and lower plate members being sufficiently long and defining therebetween an opening sufficiently wide and long to receive a multiplicity of flooring planks in close side-by-side engagement. At least one of the plate members is bowed towards the other so as to provide a tight frictional engagement with one surface of the planks present therein. The upper and lower plate members are provided with means for securing and tightening the ends thereof together at a location adjacent the outermost plank contained within the clamping member.