In design of micro-reactor for gas-liquid reactions topic, it is needed to well known the flow pattern of 2 phases gas-liquid within canal in micro dimensional the present study investigate the effect of canal diameter and shape (round canal and rectangular canal with aspect ratio I) to flow regime transitions for 2 phases flow. The experiment will be conducted with the diameter ranging from 0,6-1mm, the variables of gas and liquid velocity range from 0,1m/s - 100 m/s and 0,01 m/s - 10 m/s respectively. The flow patterns: bubble, slug, slug annular, annular, and churn are observed by CCD camera. The result will be compared with the Damianides and westwater correlations and also Weisman correlations. Flow regime transition fo 2 phases flow at variables gas and liquid velocity are presented in the experiment.