In our previous paper (Miyahara et al., 2007), the splitting of single bubbles by the liquid flow through a Raschig ring packed bed was investigated for the production of fine bubbles, including micro-bubbles, which are effective for chemical reactors and for water purification in rivers, lakes, marshes and dam lakes or fishery cultivation because of the good liquid mixing and the increase in mass transfer rate. In the present study, experiments were performed to produce fine bubbles, including micro-bubbles, using a Raschig ring packed bed under a variety of gas flow rates and six kinds of liquids. As a result, micro-bubbles less than 1 mm in diameter were confirmed with increasing liquid velocity and liquid viscosity and decreasing surface tension of liquid. Correlation equations for volumetric mean bubble diameter of split bubbles were presented as a function of gas Reynolds number, liquid Reynolds number, size of Raschig ring and Morton number. Furthermore, the measured bubble size distribution was found to be well represented by an upper limit log-normal probability function with two constants and only one variable, the maximum stable bubble diameter, as described in our previous paper (Miyahara et al., 2007).