In petroleum engineering applications, T-Junction is used as a flow separation device. The division of gas/liquid flows at T-junction results in separation of phases. However, uneven distribution of phases and excessive liquid carryover happens frequently, causing significant liquid choke for downstream equipment. To date, the most of experimental work conducted on two phase separation has been performed on the horizontal regular and reduced T-junction at stratified and annular flows. This research paper reports the investigations of two phase flow (water and air) in regular and reduced T-Junctions in slug flow regimes. The diameter ratios of 1, 0.67 and 0.50 have been selected. The gas superficial velocity is 0.33 m/s, six liquid superficial velocity has been varied from 0.47 - 0.54 m/s. comparison has been made by increasing the liquid superficial velocities and also by changing the diameter of the side arm under slug flow regime. It has been observed that liquid carry over can be reduced by increasing the superficial velocity of liquid and reducing the diameter of the side arm by keeping the side arm in the vertical upward direction. © 2018 Author(s).