In the present work, the formation of liquid drops by dripping at a micro-scale T-junction with a square cross-section (90 x 90 mu m(2)) was examined. The drop formation process consists of three stages: X-Y and X-growth stages and a detachment stage. In the X-Y growth stage, the tip of the disperse phase grows both in the longitudinal (X) and lateral (Y) directions to form a bulged shape until a maximum value of Y is reached. Then, in the X-growth stage, the bulged part continues to grow but only in X-direction, followed by the detachment stage to be separated out a single drop through a rapid necking process. The entire process is repeated at regular intervals. The volume of the drop is determined by the Y-directional size of the bulged part at the end of the X-growth stage (S(E)) and the detaching time (Delta t(Detach)). Based on the measurement and a simple scale analysis, a correlation to represent the drop size was proposed with the flow rates and fluid properties taken as parameters, and physical interpretations on the correlation were provided as well. (C) 2010 Elsevier Inc. All rights reserved.