Visualization experiments were carried out in the present study to investigate formation and detachment of the bubbles developing from an immersed micro-orifice on a plate in a stagnant and isothermal liquid. A sub-fitting method was proposed to describe the bubble edges and to extrude the bubble characteristics. Taking the microscale effect into consideration, the dynamic behavior of bubbles emerging from various orifices with 0.5, 0.12 and 0.054 mm in diameter was analyzed and compared. The experimental results showed that the bubble waiting time, departure time and departure volume decreased with decreasing orifice diameter. Based on the analysis on actual gas flow rate at the orifice, the evolution of bubble formation process was described by three or four stages for different orifices. The bubble formation under the condition of 0.5 mm orifice mainly experienced the nucleation stage, while the steady growth stage was the dominator for the micro-orifices with 0.12 and 0.054 mm in diameter. The rupture scene and evolution of bubble contact ring at the detachment moment were found to significantly vary with the orifice diameter. The inrush of several trailing bubbles into the detached leading bubble was observed for the orifices with 0.12 and 0.054 mm in diameter, resulting in a significant fluctuation in the interface. (C) 2012 Elsevier Ltd. All rights reserved.