An atmospheric pressure plasma jet using radio-frequency (rf) (13.56 MHz) power is developed to produce a homogeneous glow discharge at low temperatures (between 50°C and 150°C on the inner electrode). Discharge parameters (power, voltage, current and the phase angle) are measured and the influence of the operating parameters on the discharge characteristics is investigated for a He/O2 gas mixture. By varying the input power, a ‘phase saturation’ region and the ‘arc failure’ mode are identified. The optimized flow rate ratio between oxygen and helium is found to be 0.1/40 slpm in our experiment. At this ratio, a low power consumption and wide operational range for rf power (200 W) are obtained.