Abstract : The dynamics of discrete slugs is investigated experimentally in microchannels with rectangular cross-sections. The slugs are driven by air introduced at constant pressure. Two geometries are considered : a straight channel and a Tshaped junction. For the straight case, we assume a bulk viscous dissipation of Poiseuille's kind and determine the dynamic pressure jump at the interfaces of slugs made of wetting or partially wetting liquid. The results show similarities with studies on cylindrical tubes. For the slugs of wetting liquid, the capillary pressure drop varies with the capillary number at the power 2/3 whereas in partial wetting, the relationship is more complex especially because of the existence of a threshold pressure due to contact angle hysteresis. Next, we study the behavior of a slug of wetting liquid at a T-shaped junction. Three behaviors are observed : the splitting, the rupture or the blockage of the slug at the entrance of the bifurcation. The corresponding threshold pressure and the rupture-splitting criterium are modelised. Last, the present work leads to the knowledge of propagation laws for slugs travelling in straight channels or crossing T-junctions. These results may be useful in understanding and modeling the dynamics of droplets inside networks of microchannels.