Abstract We report experimental studies of the deceleration of Ar9+ ions within a single tapered glass capillary with an inlet diameter of 1 mm, an outlet diameter of 0.15 mm and a length of 45 mm. In the experiments we have chosen an incident ion energy of q · 8.5 keV (q – ion charge state). The influence of the deceleration potential between entrance and exit of the glass capillary on the intensity of the transmitted ion beam was measured. We detected a transmission of the ion beam up to a deceleration potential of 7 kV. Hence, the ion beam was decelerated and compressed to a diameter of 150 μm without using any additional decelerating lens systems.