The initial description of Incisivosaurus by Xu et al. showed that the skull, which measures approximately 10 cm (3.9 in) in length, preserves the most complete dentition known for any oviraptorosaurian. Their cladistic analysis indicated that Incisivosaurus lies at the base of the oviraptorosaurian group, making it more primitive than Caudipteryx and the oviraptorids. A subsequent study by Osmolska et al. in 2004 described the distinguishing skeletal features of Incisivosaurus, including a long snout that made up about half the total length of the skull, a slender lower jaw with a long fenestra (opening), and its distinctive, large, flattened front teeth. In addition to these unique features, Incisivosaurus shared many traits with more typical oviraptorosaurs, allowing its classification with that group. Several features, including its numerous teeth (most advanced oviraptorids were toothless), show that it was a primitive member of the group, and several features of the skull even support a relationship with the therizinosaurs, another theropod group that was probably herbivorous.
In 2009 the holotype skull was scanned and analyzed in three dimensions. The results indicated that Incisivosaurus had less bird - like air spaces in the skull bones than later oviraptorosaurs did. It also found that Incisivosaurus had reduced olfactory lobes and expanded optic lobes similar to ornithomimosaurs. It suggested that the most birdlike features of oviraptorosaurs may have been convergent with birds.
Incisivosaurus is assumed to have been feathered like most other maniraptoran theropods. Its total body length has been estimated at just under 1 meter (3.3 feet). It is possible that Incisivosaurus is the same species as Protarchaeopteryx, though more fossil specimens are needed before the two can be directly compared.