The effect of fines content in fluid catalytic cracking (FCC) catalyst on bubble properties was investigated by considering two catalyst batches. One contained fewer fines and had a Sauter mean diameter of 83 μm while the other had a higher fines content with a 74 μm mean diameter. The hydrodynamics were analyzed in a two-dimensional fluidized bed with superficial gas velocities in the bubbling regime. Photos of the bed were analysed by isolating bubble images, after which colour images were converted to binary images by using MATLAB® software. These binary images were used to determine properties such as equivalent bubble diameter, gas fraction, circularity and bubble hold-up in the bed as function of superficial gas velocity and fines content. The results showed that bubble diameter increases with gas velocity for both catalyst batches. A smaller bubble size was observed at all except the highest superficial velocities for the catalyst batch with the higher fines content. However, the high fines content catalyst had a higher gas fraction than the low fines content batch at all gas velocities. This average value was the same regardless of gas velocity, while an increase in superficial velocity resulted in an increase in gas fraction for the lower fines content catalyst. The bubble hold-up for the catalyst batch with the lower fines content was also higher than that of the high fines content catalyst. For both batches an increase in bubble hold-up with velocity was observed. Similar circularity values for both catalyst types were calculated at all superficial velocities.