Abstract:  A new species of the avian Sapeornis is described based on a specimen discovered from the Early Cretaceous lacustrine Jiufotang Formation in Dapingfang, Chaoyang,Liaoning Province, Northeast China. The new species Sapeornis angustis is relatively small compared to the type species, S. chaoyangensis, and distinguishable from the latter in possessing 5–6 sacrals, a distinct narrow humeral deltoid crest with a less acute dorso-distal process, narrower furcular rami, a shorter hypocleidum, a relatively longer Metacarpal I and a shorter pubic symphysis. Like in Archaeopteryx and other known specimens of Sapeornis, the new species preserves no uncinate process or sternum, suggesting that both structures are ossified in a late stage of development and none of the known specimens of Archaeopteryx and Sapeornis is fully adult. The discovery of a new species of Sapeornis provides more anatomical information about this basal avian, and documents the trend of size increase and some morphological specializations in its evolutionary history. Furthermore, it also adds to our understanding of the differentiation and diversity of birds in the Early Cretaceous terrestrial ecosystem.