An in-line slide dimming switch includes a switch and dimming circuit installed on a printed circuit board (which is installed in the in-line slide dimming switch) and operated with a dimmable energy-saving fluorescent bulb and a dimmable LED bulb, so that the in-line slide dimming switch may adjust the light emitting brightness of the dimmable energy-saving fluorescent bulb and the dimmable LED bulb installed onto a lamp holder. With the wire holders installed at both ends, a power cable is installed conveniently to achieve the effects of shortening the assembling procedure, and improving the assembling efficiency and the market competitiveness.