The potential of Liquid-liquid slug break up in a microchannel T-junction has been demonstrated in various fields. However, the phenomenon is still not well-studied. In this research work, characterisation of liquid-liquid slug break up was carried out in a glass microchannel T-junction using tetradecane as disperse phase and acetonitrile as continuous phase, observed under microscope and recorded by high speed camera. The break up phenomenon is characterized by a force ratio, R_f, which is the ratio of shear force between both phases to the combination force of continuous phase upstream pressure and capillary force. Preliminary analysis on 2D experimental images suggested that at relatively low effective Webber Number, (We_eff <3.5 e-4), disperse phase slug break up occurs at the corner of the T-junction with a clean snap off, dominated by the combination of continuous phase upstream pressure and capillary force (R_f = 1.4 ~ 2.0 e-6). At intermediate (3.5 e-4 < We_eff < 8.0 e-4), the break up occurs from disperse phase connecting neck, slightly away from the corner, in which the break up is dominated by both shear force and combination of continuous phase upstream pressure and capillary force (R_f = 2.0 ~ 3.0 e-6). A disperse phase laminar flow region is formed in the main channel at relatively high We_eff (We_eff> 8.0 e-4) in which the slug break up from the front of the laminar flow region is dominated by shear force applied by the continuous phase flow on the region (R_f > 3.2 e-6). The role of shear force becoming more important as We_eff increases because large liquid-liquid contact area.