Abstract: A device for varying stitch tightness for hosiery knitting machines, particularly for circular knitting machines, which comprises a movement adjuster connected to a slider that can slide in the cam box of the machine and supports a knockover cam of the machine. The movement adjuster comprises an actuator, connected to an adjustment cam and actuatable so as to turn the adjustment cam about its own axis through preset angles. The adjustment cam has a single external active profile, two cam followers being arranged on the slider to make contact with the active profile of the adjustment cam in two spaced points and cooperate in determining a bilateral coupling with the adjustment cam.