Eosipterus is an extinct genus of pterosaur from the Early Cretaceous of Liaoning, China.
The genus was named in 1997 by Ji Shu'an and Ji Qiang. The type species is Eosipterus yangi. The genus name is derived from Greek eos, "dawn" and Greek pteron, "wing" with a Latin ending; and a grammar error: normally the combination would have resulted in "eopterus". The "dawn" element refers to its age but also to China being "in the east". The specific name honours paleontologist Yang Daihuan.
The genus is based on holotype GMV2117, found near Jinggangshan in western Liaoning Province, in the Yixian Formation. It was the first pterosaur discovered in that region. It consists of a partial crushed skeleton of a subadult individual on a slab, lacking skull and neck. Most vertebrae have been severely damaged and even their number cannot be determined. The authors state that eighteen detached belly ribs are present in the matrix.
The wings are robust and elongated. The wing finger has the standard four phalanges, a difference from the possibly related Beipiaopterus which has lost the fourth phalanx. Total wingspan was about 1,2 metres. The pelvis is not well preserved. The femur has a length of six centimetres; the tibia of 96 millimetres. The fibula is strongly reduced. The foot claws are slightly curved; the fifth toe has been reduced to a single claw.
The authors placed Eosipterus in a general Pterodactyloidea incertae sedis; in 1999 a placement within Pterodactylidae was suggested and even a synonymy with Pterodactylus within a hypothesis that the lower Yixian Formation dated from the late Jurassic. A cladistic study in 2006 found that it was a member of the Ctenochasmatidae — David Unwin thought it more precisely belonged to the Ctenochasmatinae — but a later study showed that it was basal to the Germanodactylidae.