Description of a new enantiornithine is presented on the sufficiently complete skeleton from the Upper Cretaceous of South Mongolia. It was a small, toothless and perfectly flying bird of arboreous adaptations. Its relationships are defined within a number of Cretaceous enantiornithines, which are known recently from almost entire continental Cretaceous. All known Enantiornithes have been examined. The phylogeny of enantiornithine birds is suggested, and relationships of Enantiornithes with the other birds is justified.