Xu et al. estimated its length at , a height of and the weight at , but Xu et al. infer that "Gigantoraptor" reached its young adult size within seven years and was still at relatively early young adult stage at the time of death, and estimate that a full-sized "Gigantoraptor" is considerably heavier than . Nevertheless, "Gigantoraptor" was an enormous animal with an estimated length of and a massive weight of . The preserved mandible of "Gigantoraptor" is fused into a broad shovel-like shape, indicating that the unknown skull was over half a metre long and toothless also, probably equipped with a horny beak. The anterior caudal vertebrae have very long neural spines and are heavily pneumaticised with deep pleurocoels. The middle section of the relatively short tail is somewhat stiffened by long prezygapophyses. The caudal vertebrae are lightened by spongeous bone. The forelimbs are rather long because of an elongated slender manus. The humerus is bowed outwards to an exceptionally large extent and has a very rounded head. The first metacarpal is very short and carries a strongly diverging thumb. The hindlimbs are relatively elongated, a trait also mentioned by Holtz. The femur is slender with a distinct head and neck, measuring . The pes is robust with large and strongly curved pedal unguals. No direct evidence of feathers was preserved with the skeleton, but Xu et al. discussed their likely presence on "Gigantoraptor". They admitted that despite "Gigantoraptor" being a member of the Oviraptorosauria, a group that includes the feathered species "Caudipteryx" and "Protarchaeopteryx", it might have been "naked" because it is three hundred times as massive as these species, and very large animals may rely more on mass for temperature regulation, losing the insulating coverings found on their smaller relatives. However, they suggested that at least arm feathers were probably still present on "Gigantoraptor", since their primary functions, such as display and covering the eggs while brooding, are not related to the regulation of body heat. According to Xu et al. 2007, "Gigantoraptor" can be recognised by the following traits: reduced mandible with 45% less length compared to the femur; anterior caudal vertebrae with elongated neural spines and posteriorly located stocky, rod-like transverse processes; dentary with elongated postero-ventral process reaching to the level of the glenoid; reduced posteriorly tapered retro articular process much deeper than its wide; anterior and middle caudal vertebrae with a large pneumatic opening on the ventral surface; dentary with two fossa on the lateral surface and close to the external mandibular fenestra; anterior caudal centrum with postero-ventral margin extending ventrally; advanced laminal system of the anterior caudal vertebrae; vertical prezygapophyseal articular facets located proximal to the distal end of the process in the middle caudal vertebrae; scapula with prominent convexity ventral to the acromion process on the lateral surface; reduced calcaneum obscured from anteriorview by the expanded astragalus; distal tarsal IV with proximal projection on the lateral margin; anterior caudal vertebrae composed of opisthocoelous, amphicoelous and procoelous; pleurocoels present on most caudal vertebrae; anterior caudal vertebrae centrum with a pair of vertically arranged pneumatic openings on the lateral surface; bowed humerus with a prominent, spherical top and a curved delto-pectoral crest; proximal section of the humerus with a centrally constricted thick ridge running along the posterior margin; sub-circular, concave proximal articular surface present in the straight ulna; metatarsal III with ginglymoid distal end; constricted proximal articular surface and two lateral splines present in the pedal unguals; radius featuring a sub-spherical distal end; convex medial margin of the proximal end and a medial condyle three times elongated and extending further more distally than the lateral one on the distal end of the metacarpal I; prominent dorso-lateral process on the proximal end and a longitudinal spline on the ventral margin of the proximal third of the end in the metacarpal II; narrow spline-medial to the trochanteric head extending down to the posterior margin of the femoral end, and a patellar spline present on the anterior surface of the distal end; manual unguals with triangular lateral splines; pubis laterally compressed; femur with straight end; neck tightened between the postero-medially oriented spherical femoral top and the anteroposteriorly expanded trochanteric crest that is more stocky and higher anteriorly than posteriorly.