A blade driving assembly for an adjustable hair clipper of the present invention comprises a movable blade holder, a spring means, a spring holder and a push lever. The spring means is disposed with a coiled portion secured on the spring holder, a first portion which exerts pressure upon the movable blade holder to bias the movable blade towards the stationary blade and a second portion which biases the spring holder towards a retracted position. The spring holder is disposed with a connecting means at a front end thereof and a securing means at a rear end thereof for securing the coiled portion of the spring means, and the connecting means interlocks with the movable blade holder in such a way to allow the movable blade holder to move in a lateral reciprocating manner. The push lever is driven to move forward or backward by an external force, and a front end of the push lever abuts against the rear end of the spring holder in such a way to push the spring holder forward when the push lever is driven forward, and when the push lever is driven backward, the spring holder is biased by the spring means to retract until the rear end thereof abuts against the push lever.