To estimate mass transfer rate during bubble formation at an orifice, a theoretical model is proposed for soluble gas bubble formation in liquid by modifying the non-spherical bubble formation model. The absorption rate from pure SO2 gas bubble to water is experimentally measured as well as bubble shape and growth rate. Mass transfer from the gas-liquid interface during bubble growth is described well by the penetration theory. Experimental bubble shape, bubble volume at its detachment from an orifice, growth rate and mass transfer rate are estimated well by the present model.