Characteristics of bubble driven wakes were investigated in a simulated GTL process(0.102 m × 1.5 m in height) with viscous liquid medium. Effects of gas velocity(0.04 ~ 0.12 m/s) and liquid viscosity(0.001 ~ 0.050 Pa·s) on the wake characteristics such as rising velocity, frequency, size and holdup were determined by employing a resistivity probe method. The wake phase formed behind the rising multi-bubbles as well as single bubbles were detected effectively from the conductivity fluctuations measured by the probe. Compressed, filtered and regulated air and aqueous solutions of Carboxy Methyl Cellulose(CMC) were used as a dispersed gas phase and a continuous liquid medium, respectively. It was found that the rising velocity and size of wake phase increased with an increase in gas velocity or liquid viscosity. The holdup and frequency of wake phase increased with increasing gas velocity due to the increase of gas input into the process with increasing gas velocity. However, the values of holdup and frequency of wake phase decreased with increasing liquid viscosity, since the size of bubbles and thus that of wakes increased with increasing liquid viscosity. The ratio of wake holdup to that of gas phase, which was in the range of 0.25 ~ 0.48, increased with an increase in liquid viscosity but decreased with gas velocity. The wake characteristics were well correlated in terms of operating variables within this experimental conditions.