An adjustable slider of a window regulator includes a base body configured to connect with a cable of the window regulator and a clamp-plate assembly having first and second jaws configured to clamp a windowpane therebetween. A hinge plate supports the clamp-plate assembly. A first adjustment mechanism pivotally connects the hinge plate to the base body such that the clamp-plate assembly and the hinge plate are pivotal relative to the base body allowing a vertical angle of the clamp-plate assembly to be changed. The first adjustment mechanism is actuatable to move the hinge plate relative to the base body in a fore-and-aft direction allowing a fore-and-aft position of the clamp-plate assembly to be adjusted.