AbstractThe aim of our research was to get insight into the molecular mechanism of binding atosiban, a strong selective oxytocin (OT) antagonist by OT receptor (OTR) versus vasopressin V1a and V2 receptors (V1aR and V2R, respectively). The docking of ligand and interaction with receptor are dynamic events and Molecular Dynamics (MD) seems to be a proper tool for studying the mentioned processes. Therefore we describe MD of three pairs of atosiban‐receptor complexes, two complexes per each receptor, conducted in the fully hydrated 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphatidylcholine lipid bilayer, simulating G protein‐coupled receptors environment. We confirmed strong and specific binding of atosiban in OTR and a weaker binding of it in V1aR, on the contrary to its less specific binding in V2R, in the agreement with our preliminary results [Ślusarz et al. 2003].