Shell and tube type of heat exchangers are widely used in many applications. Understanding on the cross-flow over tube bundles in a shell is not well established due to the flow complexity and difficulty in measurement, especially in the case of two-phase flow. More detailed and accurate velocity data are needed in order to establish reliable design and optimum performance for tube bundle models. This study was aimed at clarifying the structure of bubbly cross-flow over tube bundles by obtaining detailed velocity data using Particle Image Velocimetry (Hy). Experiments were conducted on two types of model, in-line and staggered tube bundles with pitch-to-diameter ratio of 1.5, containing 20 rows of five 15 mm O.D. tubes in each row. The images of liquid flow and bubbles were distinguished by optical filtering and image processing techniques. The velocities of liquid flow and bubbles were measured successfully and characteristics of the bubbly cross-flow were clarified.