A lot of research has been conducted on the gas injection methods; especially bubble formation from the upward orifice or nozzle, whereas few studies on bubble formation from the downward nozzle have been reported. In this study, the effects of both nozzle shape and diameter on the bubble formation mechanism from the vertically downward nozzle were investigated. The theoretical results obtained by applying the revised two-stage spherical bubble formation model for the downward nozzle was compared with the experimental results for small metal downward nozzles. The bubble formation mechanism and the bubble size were influenced by the edge angle and diameter of the nozzle, respectively, and the gas flow rate.